一个被忽视的问题：怎么换水？ 译自RC

花匠鱼

换水，我估计大家基本的认同是养海缸必须是要换水的，不像淡水缸，也许一两年都不用换水。因为海水缸实在太复杂了，里面涉及到的元素多到数不清，而且极大多数是我们鱼友所不能测量和控制的。不过大家各自换水的方式估计是千奇百怪的，各有各的理由当然。

就我个人来说，之前一直都是2个星期换水80升，大约10%，但是感觉每一次换水都是一次负担，看到换水真的很头疼。而且每次换水进去，感觉对缸都是一种冲击，生物有负面反应，当然有可能是因为我盐水比较新比较生，而且也没有严格对温。

前些天看到了这个文章（其实很早就看到了，但是很长我都没心思看，所以也没有了解它的意思），于是想验证一下如果我进行少量多次换水，对于鱼缸来说到底效果多大，跟大量换水有多少差距，有什么优劣。当然，是要用数据说话不能只是凭感觉。文章是RC上的权威Randy Holmes-Farley写的。

我英语并不好，看英文文章很累，如果说看这篇文章，从头看到尾一个字不漏我估计要1个小时。后来我想既然要花一个小时看完，我还不如花3个小时把它翻译出来，分享一下。结果他妈的翻了我3天，当然，有工作要做不能一天到晚搞这个。下面是原文，请大家看一下，如发现有翻译错误的请指正！


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http://www.reefkeeping.com/issues/2005-10/rhf/index.php

Water Changes in Reef Aquaria

Water changes are, by definition, the act of replacing some aquarium water with "new" water. For various reasons, the ways to perform them and their importance are both a matter of some debate and confusion in the world of reef aquaria. Many aquarists perform them extensively, and others never do them. For those who do, the reasons vary and are sometimes even at odds with one another; for example, replenishing "trace elements" and exporting built up "impurities," with the identities of these two being unclear and possibly overlapping.
换水，顾名思义就是用新水去替换部分老水。因为很多原因，换水的重要性和换水的方法，一直是世界范围内鱼油间疑问和讨论的内容。很多鱼友大量的进行换水工作，而有些鱼友则从不换水。对于那些换水的鱼友来说，支持换水的理由也是各不相同，比如说：补充微量元素，或者排出老水中部分杂质和营养盐。

Much of the confusion about water changes stems directly from uncertainty about three things:
1. What is in the existing aquarium water.
2. What is in the new aquarium water.
3. What levels are optimal for different species.
While several authors have endeavored to more clearly answer these three questions (links to which are given in the references), the questions are really very complicated. Unfortunately, this article will not help to clarify these issues.
很多关于换水的疑问，直接来源于对以下3样东西的不确定：
1，缸水中有什么
2，新水中有什么
3，对不同的生物来说，什么水质合适
很多人试图去回答这三个问题（底下有连接），不过这几个问题确实非常的复杂，不幸的是本文并不能帮助问答这些问题。

What this article does provide, however, is a clarified understanding of what water changes are capable of achieving. Using known or calculated rates of addition and depletion of a variety of chemicals in seawater, the effects of water changes can be readily modeled. The impact of water changes on calcium, alkalinity, magnesium, nitrate and sulfate, for example, are shown graphically. In several cases, these examples also serve to provide guidance as to what is occurring with other ions not modeled, but which would increase or decrease in a similar fashion. For example, the control of nitrate accumulation with and without water changes can also show what effect water changes have on other accumulating generic chemicals such as phosphate, organics, heavy metals, and other materials.
本文可以提供的，是换水可以带来怎么样的效果。利用已知的，缸内消耗的以及添加的各种化学元素，换水的效果可以计算出来。换水对于缸内元素比如钙、镁、KH、硝酸盐和硫酸盐的影响，本文用图表列出。另外有一些图表，也可以用来判断其他元素由换水带来的影响，比如说：硝酸盐在换水和不换水情况下累积情况的图表，也可以用来判断其他容易累积的化学成分比如说磷酸盐、有机物、重金属等。

How much water must be changed depends entirely on what the desired outcome of the water change actually is. If it is to reduce an accidentally added toxin, massive, immediate and repeated water changes may be appropriate. If it is to maintain calcium and alkalinity, large daily water changes may be necessary. If it is to keep slowly added or depleted ions (e.g., magnesium or strontium) from drifting away from "normal" levels, then smaller changes may be adequate.
到底需要换多少水，这完全由你换水想要达到的换水结果来决定。如果说是为了降低某种不小心添加进去的毒素浓度，那么就需要尽快、极大量的换水。如果是为了维持钙或KH，那就需要每天、较大量的换水。如果说为了维持那些消耗量不大的元素比如镁或锶，那么较小量的换水就够了。

Previous articles on water changes have "shown" that small water changes are not useful, and have sometimes left the impression that even many small water changes are not beneficial. It is also "common knowledge" among many reef aquarists that continuous water changes (where water is added and removed at the same time, usually by automatic pumping) is not very useful "because this removes some of the new water that was just added." As I'll show, these assumptions do not stand up to analysis for typical water change scenarios. Consequently, whether choosing to change a lot of water, or only a little, and whether it is done continually, daily, or only rarely, more water change options are available to aquarists than many realize. These increased options' availability may permit busy aquarists to spend time on other important activities, and less time on water changes, while still accomplishing the same goals.
以前的文章曾说过小量换水没什么作用，给人的印象就是即便是持续多次的小量换水也没什么用。另外还有一个普遍认识就是：同步换水（也就是一边抽老水，一边加新水，同步进行）也是没什么效果的，因为“这个过程中会有不少新水刚放进缸里就被抽走了”。下面我也将证明，这些假设在经过仔细分析后也站不住脚。因此，不管是选择什么方式换水，大量的，或者少量的，或者持续的，或者每天换，或者不经常换，其实换水有很多种可行方式，比大家想象的要多。对于那些比较忙的鱼友，也有可用的换水方式，让他们把较少的时间花在换水上，但也能达到同样的效果。

This article is divided into the following sections:

Contents:

本文分一下章节讨论：

目录：

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Introduction
简介
What Can be Accomplished with Water Changes
换水可以达到什么效果
Monthly Batch Water Changes: A Nitrate Example
每月换水：以硝酸盐为例
Size of Water Changes: A General Case
换水量：通用范例
Size of Water Changes: A Nitrate Example
换水量：以硝酸盐为例
Water Changes to Add Something: Magnesium
通过换水补充元素：镁
Water Changes to Add Something: Calcium and Alkalinity
通过换水补充元素：钙和KH
Very Large Water Changes Maintain Calcium and Alkalinity
很大量的换水来维持钙和KH
Water Changes to Deplete Something: Sulfate from a Homemade Two-Part Additive
通过换水排出元素：DIY钙镁KH补充液中的硫酸盐
How to Perform Water Changes
怎样换水

Large Batch Water Changes
大量换水
Small Batch Water Changes
小量换水
Continuous Water Changes
连续换水
Conclusion
总结
Additional Reading Related to Water Changes
关于换水的扩展阅读

花匠鱼

What Can be Accomplished with Water Changes
换水可以达到什么效果

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Water changes can typically accomplish two things. These are:
To raise the concentration of a depleted "something" that is at a higher concentration in the new water
To reduce the concentration of an elevated "something" is at a lower concentration in the new water

换水通常可以达到两个目的，它们是：
1，提升老水中消耗掉的东西，因为新水中含量较高
2，减少老水中积累的东西，因为新水中含量较低

Depending on what is being added, a variety of materials can accumulate in reef aquaria. When supplementing calcium, alkalinity and magnesium, these accumulating substances can include chloride, sulfate, sodium and a host of inorganic and, in some cases, organic impurities in the supplements. From foods, certain metals can build up (copper, for example) as well as nitrogen and phosphorus compounds (nitrate and phosphate, for example). Top-off water can contain a variety of inorganic and organic compounds, and can be a big source of certain ions (silica, copper, etc) if not purified. Even the activities of the aquarium inhabitants themselves can cause the buildup of various materials, such as organic compounds (toxins, metabolic byproducts, etc).
因为我们需要往鱼缸里扔东西，很多种物质都会在鱼缸里不断累积。比如说我们要添加氯化钙，氯化镁，硫酸镁或者碳酸氢钠来维持大量元素，那么氯离子，硫酸根离子，钠离子，以及其他一些有机或者无机杂质，都会在缸里累积。比如说我们需要喂食，那么可能会带来铜离子的累积，另外当然还有硝酸盐和磷酸盐。就连自动补水缸里的RO水，如果净化质量不高的话，也可能是很多有机或无机物质的大量来源，比如硅和铜。还有缸内的生物，也会产生很多物质造成堆积，比如新陈代谢物或者毒素等等。

Some of these impurities may be well removed by other mechanisms, and some may be well removed only by water changes. The buildup of chloride or sulfate, for example, is not readily countered by any means except water changes (although dialysis type devices can theoretically accomplish the task).
其中有些杂质可以部分被缸内设备移除（蛋分或者活性炭等等），而有些只能通过换水来部分移除。比如氯离子和硫酸根离子的堆积，除了换水基本上就没有别的办法了（除了使用非常专业的透析设备可能可以达到效果）。

Aquarists also often rely on water changes to add ions that are being depleted from the aquarium. Magnesium is a common example; strontium may be another. Many aquarists speak of trace elements being added, but in many cases it is not clear whether new salt water has more, or less, of many trace elements in each of their many different forms (iron, for example).
鱼友也经常通过换水来维持水中消耗的某些元素的浓度，比如镁，还有锶。也有很多人提到微量元素，不过也没有技术手段可以明确判断到底是否新水中的微量元素更多。而且微量元素通常以很多种形态存在，比如铁。

In a certain sense, if an aquarist is comfortable with whatever is in the salt water being used, then it doesn't really matter if it contains any particular material at a higher or lower concentration than the aquarium, because the water change will pull it in the direction of the new water. Of course, the size of the effect will depend entirely on how different the new water is from the old, and what portion of the aquarium water is changed.
某种程度上说，鱼友如果对于新水感到满意（比如开缸时候），那么也就不需要去管它新水中什么元素到底是比老水中浓度高或者低，因为，只要是换水，反正是在将水质往着新水的水质去。当然，这种效果的程度完全取决于新水和老水的差异程度，以及换水量。

Without building too much of a case for water changes without a lot of solid information about the three questions listed in the introduction (i.e., what is present in the new and old water, and what is optimal), I will assert that I believe that water changes are beneficial. I do not believe that they are the most useful way to reduce nitrate or phosphate (although they are much better than nothing, as shown below), but they are a good way to reduce organics that are not readily skimmed or bound to activated carbon. Water changes also help export excess metals that build up over time. Copper, for example, tests higher in my aquarium than in the salt mix that I use (Instant Ocean). Finally, water changes aid in keeping the major ions in appropriate ratios, despite the skewing that may come from foods, additives and deposition processes such as calcification (several of which are modeled below).
抛除大量的模型计算，和简介中3个问题的答案，我至少主张换水是有利的。我并不相信换水是降低硝酸盐和磷酸盐最好的办法，但是换水是排除有机物的好方法，因为蛋分或者活性炭也很难排除它们。换水也可以多少排除累积的重金属比如铜，在我的缸里铜浓度就比新水里测到的高，我用Instant Ocean盐。（也就是国内称红十字小丑盐——译者）。另外，换水帮助保持大量元素的适当比例，

The sections that follow specifically deal with how water changes of various types and sizes can impact these various goals.
下面的章节着重讨论各种形式、数量的换水，会带来什么样的结果。


Monthly Batch Water Changes: A Nitrate Example
每月换水：以硝酸盐为例

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The simplest water change method to analyze also happens to be a common practice: simple batch water changes performed once a month or so. In this method, an amount of water is removed from the aquarium, and is quickly replaced with new water. There are drawbacks to this method that are discussed in the summary (such as matching the temperature when the change is above 5-10%), but it is the method used by most aquarists.
我们要分析的最简单的一种换水模式，也是我们日常最常见的一种换水方式：也就是一个月换一次水。这种方法是我们把缸里的老水抽出一定量，然后马上用同等量的新水替换进去。这个办法有一些缺点，比如说需要对温（比如换水量超过5%-10%的时候）。不过这种换水方法是被鱼友们最为广泛使用的。

Figure 1 models the depletion of an impurity present in the aquarium water, provided no other inputs of that impurity are added. We can think of it as a percent of the starting impurity, or as ppm nitrate with day zero at 100 ppm, to consider a specific case. The analysis is exactly the same regardless of what the substance is, if we assume that none is added over the course of a year, and that none is generated in the aquarium. Four different water change scenarios are compared: every 30 days a single batch water change is performed of 0%, 7.5%, 15% and 30%. This range was selected to cover the values that most aquarists use, although a few may use slightly larger or more frequent changes. The model is very simple: each 30 days, the nitrate's concentration is diluted by the water change. In the case of a 15% change, for example, the concentration is multiplied by 0.85.
图1展示了某种物质的消耗状况，假设这过程中没有添加这种物质。我们可以假设比如说是硝酸盐，在第0天开始，其浓度时100ppm。不管假设是什么物质，都一样可以参考此图，只要假定在这整个过程中没有添加而且缸里也没有生成这种物质。4条线表示4中不同的换水量：每个月1次，0%，7.5%，15%和30%。基本上这些换水量可以涵盖大部分鱼友的换水量了，虽然可能有个别鱼友会使用更大的换水量。分析模型很简单，每30天，硝酸盐浓度都通过换水被稀释了。比如每月换水15%，那么硝酸盐浓度就变成每次换水前的85%，也就是浓度乘以0.85.



It is clear from Figure 1 that the larger the water change, the more rapidly the nitrate declines. This model is limited in its usefulness, however, in that many impurities are building up at the same time that they are being reduced by water changes.
从图1很明显可以看到，换水量越大，硝酸盐下降越快。同理，缸内的其它杂志也是以同样的速度在下降。

Figure 2 shows the same sort of model where nitrate starts at 0 ppm, and then is allowed to accumulate by 0.1 ppm per day (approximating values potentially encountered in typical reef aquaria, where over the course of a few months, nitrate might accumulate to 5-10 ppm). This model describes reasonably well what might take place in a reef aquarium where the starting concentration of nitrate is zero ppm.
图2显示的是类似的模型，不过硝酸盐的起始浓度是0ppm，不过与上图不同的是，这张图假设每天缸内会产生0.1ppm的硝酸盐（相当于如果不换水一两个月硝酸盐会上升到5-10ppm的那类缸）。然后，和上图一样，进行4中换水量的每月换水，可以看到整个过程中硝酸盐的累积情况。



Figure 3 shows a hybrid model where the nitrate level is initially high (100 ppm) and is allowed to accumulate at the same rate as in Figure 2 (0.1 ppm per day). In this case, it is very clear that water changes can usefully limit the nitrate concentration. Presumably, this sort of situation is the driving force behind water changes in many fish-only aquaria where nitrate buildup is a major concern, where the other nitrogen export methods are not as often used as in reef aquaria, and where especially low nitrate levels may not be as critical as they are in a reef aquarium.Clearly, larger water changes are much more effective than smaller changes for a fixed number of such changes.The 30% change per month gives a nitrate concentration of only 9 ppm after a year, while the 7.5% monthly change yields a concentration of 64 ppm nitrate after the course of a year.
图3是图1/2的混合模型，硝酸盐起始浓度为100ppm，并且每天缸内会产生0.1ppm。可以看到，通过换水，缸内硝酸盐的浓度可以得到一定的控制。这个模型切实也是很多纯鱼缸的切实模型，纯鱼缸通常主要的问题就是硝酸盐的控制。对于珊瑚缸来说，硝酸盐的控制一般并不是主要用换水来实现，通常还会有更多其它的过滤设备。
很明显，大量换水比少量换水的效果要明显很多。如果每个月换水30%，一年后这个缸从一开始的100ppm变成了9ppm；而如果每月换水7.5%，则一年后缸内还是有64ppm的浓度。




在这个分析模型里，很不幸，可能看起来固定次数的小量换水，没有大量换水来的有效。但是，不要忘了，换水次数并不是一定要固定比如1个月1次的。下面的章节，我们将看到固定体积的小量换水，也能像大量换水一样有效。

花匠鱼

Size of Water Changes: A General Case
换水量：通用范例



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As shown in the previous section, a fixed number of small water changes is not as beneficial as the same fixed number of larger water changes. However, for an aquarist who wants to do water changes, the decision of how to change the water should not be driven by that analysis alone. The conclusion of such an analysis is different if one assumes that the aquarist has a fixed volume of water to change, and is just deciding how to accomplish it.
如上节所述，定期小量换水不如定期大量换水有效。但是，鱼友不能光凭上面的分析来决定换水方式。

For example, with a 100-gallon tank and a goal of changing 30 gallons each month, one might consider changing 30 gallons once, 15 gallons twice, 10 gallons three times, 5 gallons six times or 1 gallon 30 times. In the extreme case, we can imagine changing an infinitesimally small amount of water an infinitely large number of times, eventually consuming the entire 30 gallons (I actually do this in my aquarium, as I'll explain).
比如说，一个100加仑（约380升）的鱼缸，目的是要每个月换掉30加仑（约115升）的水。有人可能会选择每个月一次性换掉这30加仑水，有的人可能会想分批换比如15加仑*2次、10加仑*3次，或者5加仑*6次，或者甚至1加仑*30次。甚至可以设想以极端形式，就是一次换无穷小量的水，并且每个月进行无穷大次数的换水，只要每个月总量是30加仑。（我其实就是类似这样换的，后面我会解释）

Aquarists often think that many small changes are not as efficient as one big change since some of the water in all subsequent changes was already replaced by earlier changes. This is a correct assertion, but it is often overstressed. After changing 10% three times, only 10% of the first 10% change was changed the second time (1% of the total). So the difference is small. We can mathematically calculate the efficiency of such changes as follows. If we use our 30% example, then one 30% change removes 30% of the impurities, assuming an equal distribution of the impurity within the water. If we do six 5% changes, then the reduction in impurities = 1-(0.95)6 = 26.5%. So it is less efficient (six 5% changes exactly equal 26.5% changed in one batch), but it is not radically less efficient. Going smaller still, the difference is even smaller. Doing 30 one percent changes removes 1-(0.99)30 = 26.0% of the impurities.
鱼友通常认为多次少量换水没有少次大量换水有效，因为多次少量换水的时候，后面的换水势必把之前换进去的较新的水换出来一部分。首先这个论断理论是正确的，但是其效果被高估了。比如每个月分3次每次换10%，那么第二次换水的时候其实只是把第一次换水的那10%中的10%换了出来（总水量的1%）。所以差别不大。下面我们来计算一下：假设每月1次换水30%，那么30%的杂质可以排出，这是简单的；然后，假设我们每个月换水6次每次换5%，那么有多少杂质被排出？计算是这样的：排除比率=1-(0.95)6=26.5%。确实，是不如单次大量换水有效，但是其实差别并不大。如果计算每个月30次每次1%，杂质排出率 = 1-(0.99)30 = 26.0%，跟分3次基本没什么差别。

The extreme case of infinitely small water changes done an infinitely large number of times is approximated by continuous water changes that add water at exactly the same rate it is being removed. The details of how to do this mechanically are described below. This case is a standard example in advanced math textbooks (differential equations, specifically). Assuming the aquarium is well-mixed as the water is changed, the remaining impurities are given by:

I = Ioe(-C/T)

where I is the amount of impurities present, Io is the amount present at time zero, e is the constant 2.71828, C is the amount changed, and T is the tank's total volume.  So for 30 gallons changed this way in a 100-gallon tank, the remaining impurity is 0.74 times Io, or a reduction of 25.92%.  
上面提到的极端情况也就是通过无穷大量次换水量，每次换无穷小量的水，下面我们来计算。这其实是高等数学教材上的标准范例（微积分），不过前提是每次换水之前，先前换进去的新水已经充分和老水混合了。那么杂质残留应该是：
I = Ioe(-C/T)

这里的" I "就是杂质残留比例。 "Io" 是起始杂质浓度，e是常量2.71828，C是换水量，T是总水量。所以，100加仑的缸用次方式换入送水量30加仑，杂质剩余量是74.08%，也就是25.92%残留。

The table below compares these results for a 30% water change done via different numbers of smaller changes. Clearly, the single 30% change is a little better than the others (70% vs. 72-74% initial impurities remaining), but the difference is quite small, and the difference between the others in efficiency is trivial.

下表显示了各种换水量与30%单次换水的对比，很明显单次30%确实效能最大，但是优势有限。




The same analysis can be carried out for larger water changes. Figure 4 shows a graph of the water change efficiency as a function of the size of the individual changes, when 100% of the aquarium volume is changed. Clearly, the very large changes are much more efficient. In an emergency situation when some toxin must be quickly reduced, performing two 50% changes or one 100% change is far better than doing 20 5% changes. In the normal course of aquarium husbandry, however, when, out of concern for stressed organisms, water changes that large are not normally performed, and where water changes are often in the 0-30% each range, Figure 5 shows that the efficiency does not change greatly over the range involved.
同样也可以用上述方法分析大水量换水。图4表示的就是每月100%换水量。很明显大量换水确实效率更高，在紧急情况下比如误下了什么毒素，那么分两次每次50%或者甚至一次性100%换水就比分5次每次20%有效很多。不过在日常维护中，考虑到换水对生物的冲击，大换水量一般很少用到。通常也就是每个月30%以内。图5显示，在这样的每月较小总换水量情况下，各种换水方式效果区别并不那么大。

花匠鱼

Size of Water Changes: A Nitrate Example
换水量：以硝酸盐为例



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The cases examined above for nitrate with "once a month" batch water changes can also be examined using smaller, but more frequent, changes. Figure 6 shows results obtained by doing daily batch water changes that amount to a total of 7.5%, 15% and 30% changed each month (0.25%, 0.5% and 1% daily). This graph can be compared to Figure 1, and Figure 7 shows an overlay of Figures 1 and 6. It is clear from Figure 6 that daily water changes are essentially comparable to larger once a month water changes in their reduction of existing nitrate concentrations over a year, as long as the same total volume of water is changed. It turns out that continuous water changes are so close in efficiency to daily water changes that for the sort of data shown in Figures 6 and 7, the results of continuous changes are indistinguishable from those of daily changes (which is clear in Table 1 also, where continuous changes and daily changes (1 x 30) nearly match each other's efficiency).
之前用硝酸盐为例分析了每月1次较大换水量，现在来分析少量多次换水。图6表示了每月总换水换水7.5%、15%、30%，不过平分到每天换，也就是每天换0.25%、0.5%、1%，整个图模拟了一年内的情况，可以与前面图1比较。图7则是把图1和图6合在一起。可以看到，效果基本一致。






Extending this discussion to nitrite accumulation, Figure 8 shows results when nitrate starts at zero ppm and is allowed to accumulate, when water changes are done on a daily basis. These data are comparable to Figure 2, and Figures 9 and 10 compare the two methods (daily vs. monthly) for 7.5% and 30% changed per month, respectively. Figure 11 is an enlarged version of the bottom of Figure 10. In this scenario, there is little difference between the two methods when changing 7.5% of the volume per month, but a somewhat larger difference when changing 30% per month, with nitrate averaging 1-2 ppm lower in the batch case compared to the daily case. Both are far better than no changes, being about 30 ppm lower than without water changes (after a year). Again, the continuous case exactly overlays the daily change case (not shown).
然后我们把缸内自身硝酸盐增长也考虑进去。
下图8表示了每天产生0.1ppm硝酸盐，然后进行每天0.25%、0.5%、1%换水（每月7.5%、15%、30%），可以与图2比较。




下图9比较了每月总换水量7.5的情况，红线表示等量分每天换，绿线表示每月换一次。
图10则是月总量30%，和图9类似。





下图11是将上图10放大。可以看到，无论每天还是每月一次换，月总量30%比月总量7.5%都好很多，月换水30%的锯齿形更大，不过高点还是和日换水一致。




Finally, we can model the drop in nitrate when it starts high (100 ppm) and accumulates at a rate of 0.1 ppm per day, using both daily and continuous water changes. Figure 12 shows the data for daily changes. Again, continuous water changes exactly overlay these results (not shown). Figure 13 compares daily and monthly water changes of the same total volume. Clearly, the size of the water change is not particularly important, and both daily and monthly water changes of the same total volume have a substantial effect on nitrate. Larger total volumes changed obviously have a bigger effect on residual nitrate after a year.
现在我们模拟缸内原始浓度100ppm，并每天产生0.1ppm。
下图12表示了这种情况下每天持续换水0.25%、0.5%、1%（每月总量7.5%、15%、30%）。可与图3每月1次比较，结果基本是一致的。图13把图12和图3结合在了一起更清楚。只要月总量是一致的，那么每天或者每月1次结果接近。




All of these conclusions extrapolate well to other ions that have similar properties. The graphs of dropping initial nitrate concentration (Figures 1, 6 and 7, for example) describe well the drop of any pollutant in the water that is not otherwise being added or eliminated - something that was spilled into the aquarium, for example. Simply think of the y-axis as a percent of the initial pollutant remaining.

The graphs of accumulating nitrate concentration (Figures 2, 8, 9, 10 and 11) describe the effects one might expect for other ions, starting with pure salt water. These might include metals that come from foods or top-off water, phosphate and organic compounds. Clearly, the scale of the y-axis would be different, but the effects achieved by water changes of various sizes would be similar.

Finally, the graphs of accumulating nitrate concentration where it started at an elevated level (Figures 3, 12, and 13) describe the effects one might expect for other ions when starting with already polluted aquarium water. These might include metals that come from foods or top-off water, phosphate and organic compounds. Clearly, the scale of the y-axis would be different, but the effects to be obtained by water changes of various sizes would be similar.
同样这些图可以类推到其他类似物质比如磷酸盐或重金属离子。

花匠鱼

The above analyses show how effective water changes can be at removing undesirable impurities. Water changes can also be used, however, to add ions that are becoming depleted over time. A classic example is magnesium, which can become depleted as it is incorporated into calcium carbonate that is deposited as coral skeletons, in coralline algae and in abiotic deposits on pumps and heaters.
上面的分析都是针对换水可以排除缸水中某种杂质。换水同样也可以用来补充缸中消耗的物质。典型的例子是镁，它会与碳酸钙一起被利用做珊瑚的骨骼，珊瑚藻也会使用镁，另外还会形成一些非生物沉淀堆积到泵或者加热棒上。

In previous articles I have modeled the depletion of magnesium under a variety of scenarios. The first assumes that only calcium and alkalinity are added to reef aquaria, as when using limewater, and the magnesium is allowed to deplete. In that case, the rate of depletion depends on the rate of calcification and the exact organisms depositing the calcium carbonate, since the amount of magnesium incorporated varies from organism to organism. In that article I identified three depletion rates that likely span the range experienced by many aquarists, and these are about 0.1, 0.2 and 0.4 ppm magnesium per day. So starting at a natural level of 1280 ppm magnesium, it is easy to predict what the magnesium levels will become with, and without, water changes.
之前一篇文章我讨论了镁在多种情况下得消耗情况。首先假设了只往缸里补充钙和KH（加石灰水也就是氢氧化钙），让镁消耗而不补充。镁消耗率跟钙消耗率是关联的，不过对不同的生物来说，钙镁的消耗比例也是不同的。我假设了三种镁消耗量，大概可以涵盖所有鱼友缸中的消耗情况：每天0.1、0.2和0.4ppm的镁。所以按照镁在海水中天然起始量1280ppm，可以推算在换水或者不换水的情况下，镁含量会如何变化。

Figure 14 shows the depletion of magnesium at a high depletion rate with daily water changes amounting to 0%, 7.5%, 15% and 30% per month. For most graphs in this article I have chosen to show only the results of daily changes amounting to a particular percentage per month, rather than showing all of the possibilities of continuous vs. daily vs. weekly vs. monthly for each ion. In essence, the conclusions are the same for each method, as long as the amount changed is roughly the same. In a few select cases, I show the data to support this assertion.

In order to see the differences in magnesium depletion more clearly, but at risk of exaggerating the effects due to the scale change, Figure 15 shows the same data blown up. Clearly, the water changes can effectively reduce the drop in magnesium, but only the 30% per month method keeps the level from dropping too far. Figure 16 shows a comparison of daily vs. monthly for the 30% case, and indicates that the monthly change is better, but not drastically so.

下图14显示了在每天消耗0.4ppm镁，每月总换水量0%、7.5%、15%、和30%分每天平均进行的情况下，镁的变化情况。图15则是图14放大比例尺之后的图形，看的更清楚。可以看到换水比不换水有效地防止了镁含量的下降，不过只有在每月总量30%的情况下，镁含量才不会跌的太低。图16则是在图15的基础上再加上了每月一次换水30%的对比，可以看到每月一次的话镁含量总体保持的更高些，不过差别也不大。







Lower depletion rates will, obviously, require a lesser amount of water to be changed to help overcome the magnesium drop. Figures 17 and 18 show the effects of water changes at these lower depletion rates (the scales are the same as in Figure 15). At the lowest depletion rate, even daily changes amounting to 7.5% per month are adequate to maintain magnesium above 1250 ppm after a year (1250 ppm being the lower limit of the range of 1250-1350 ppm magnesium that I recommend for reef aquaria).

如果镁消耗量没那么大，那么相应的也只需要较少量的换水来帮助抵消镁的下降。图17、18显示了在镁低消耗量下（每天0.1和0.2ppm）的情况。可以看到如果在每天0.1ppm的镁消耗量下，即便是每天换水，月总量仅7.5%的情况下，也足以在一年内将镁保持在1250ppm以上。（我推荐镁含量应维持在1250-1350ppm范围内）



final scenario to consider for magnesium depletion comes into play for aquarists supplementing calcium and alkalinity using calcium chloride and either sodium carbonate or sodium bicarbonate (e.g., baking soda, baked or not, respectively). The reason that this scenario is different from the above cases is that the addition of the chloride and the sodium ions tends to raise salinity. If the salinity is then adjusted back to normal levels periodically (by dilution with fresh water), the effect is to depress magnesium faster than in the scenarios above. I have modeled this concern in the context of my "do it yourself" two-part additive system, and have suggested that for moderate use of this system (8 ppm calcium and 0.4meq/L of alkalinity per day), the magnesium depletion may be on the order of 1.2 ppm per day. That rate is much higher than for the same amount of calcification in the scenarios above (which are designed for limewater which does not have an increased salinity/dilution effect).
最后一个模型是在以上基础上加上用氯化钙和碳酸氢钠来补充钙和KH。之所以加这些东西会有影响，是因为其中的氯元素和钠元素会少量提升总盐度。如果因此需要加淡水来将盐度降低到原来水平，那么镁含量的降速就会比上面的模型更快。我在“DIY钙和KH补充液”一问中提到了这个问题，并且建议在每天须加8ppm钙和1.12 dKH的情况下，镁的消耗量大约会是在1.2ppm。这个消耗量就比上面几个模型大多了（用氢氧化钙提升钙和KH则没有这个问题）。

Figures 19 and 20 show the effects of water changes on magnesium depletion under this supplementation method. From these graphs, it is clear that even with 30% water changes per month, magnesium is not adequately maintained at appropriate levels when using this type of supplement system. That result is why I have included Epsom salts (magnesium sulfate) as a third part in that system, despite the fact that it adds complexity and raises sulfate over time (which is also modeled below).
图19和图20显示了在这样的镁消耗量下的情况（图20放大比例）。很明显，如果是用氯化钙+碳酸氢钠补充钙和KH，即便每月换水30%，也无法将镁保持在合理的含量。这也就是为什么需要另外补充镁的原因。

花匠鱼

Water Changes to Add Something: Calcium and Alkalinity
通过换水补充元素：钙和KH



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The above model investigates what happens with respect to maintaining something that is slowly depleted, such as magnesium. Some materials, however, such as calcium, alkalinity and silica can be rapidly depleted. In these cases, normal water changes just cannot keep up with the depletion rate, as is shown in this section. Reef aquaria have a range of depletion rates for calcium and alkalinity. At the low end of reef aquarium demand, we might assume a daily depletion of 4 ppm of calcium and 0.2 meq/L (0.56 dKH) of alkalinity per day. That turns out to require the daily addition of about 0.5% of the tank's volume (1/2 gallon to 100 gallon tank) of saturated limewater to meet that demand.
上面模型分析的是通过换水来补充缸内消耗速度较慢的元素比如镁。然后还有一些元素比如钙，KH，和硅，消耗速度会很快。对这些元素来说，普通的换水并不能抵消其自身消耗速度。即便是消耗量很低的海缸，我们估计也会有4ppm钙和0.56 dKH的日损耗。这需要大约每天补充0.5%容量的（比如200L的水要加1L）饱和石灰水溶液才能补足。

Figures 21 and 22 show the drop in calcium and alkalinity, respectively, over a month when doing daily water changes amounting to 0% (no changes), 15% and 30% per month. It assumes that the saltwater being used has a calcium level of 420 ppm and an alkalinity of 4 meq/L. Neither water change rate has an appreciable impact on the calcium and alkalinity drop. In reality, the drop will eventually level-off as calcification is reduced and eventually stops as alkalinity and calcium get low enough, but especially in the first week of the model, it should approximate what happens, and it isn't pretty. Higher demand aquaria (with sometimes five times more demand or even higher in some reef aquaria) will deplete calcium and alkalinity even faster. Clearly, "normal" water changes cannot keep up.
Some salt mixes contain excessive calcium. Using a salt mix with 550 ppm calcium will make water changes more effective at maintaining calcium above 380 ppm, but it still does not work out for "normal changes" to be able to maintain calcium levels in the long term. In a low demand model (4 ppm drop in calcium per day), changing 1% daily drops the calcium level to 380 ppm by day 56. Using regular batch "once a month" changes, the calcium level drops from 550 ppm at the start to 438 ppm just before the first water change (472 ppm after it). Then, 23 days later, before the next 30% water change, it has dropped below 380 ppm. Of course, at higher depletion rates the drop is even faster (it takes only nine days to fall below 380 ppm at a depletion rate of 20 ppm per day and changing 1% per day).

图21和图22显示了月总换水量0%、15%、30%，分每天平均进行的情况下，钙和KH分别的下降。假设新水中钙是420ppm，KH为11.2 dKH。这些换水方式都无法充分补足钙和KH的消耗量。实际上钙和KH的下降速度会减慢并且最总停止下降，因为两者含量已经低到无法被生物利用。这显然是不应该发生的。高负荷的缸可能会比低负荷的缸消耗量大5倍之多。显然，正常换水是无法补足的。
有些盐钙含量超高，如果用钙含量550ppm的盐，那可以将钙保持在380ppm。但是如果用较常规的换水量，依然是无法长期保持钙含量。在低消耗的缸里（4ppm钙每天）每天1%的换水，用550ppm钙的新水，那么在第56天钙含量会下降至380ppm。如果是一个月1换水，那么第一个月换水之前，550ppm就已经降到438ppm，换水30%后是472ppm，然后23天后，在换水前，钙已经低过380ppm了。如果消耗量大的缸，下降就更快。消耗20ppm/天得缸，只要9天，而且每天换水1%，就已经下降到380ppm。

花匠鱼

Very Large Water Changes Maintain Calcium and Alkalinity  
很大量的换水来维持钙和KH

In the previous section I showed that normal water changes of up to 30% per month cannot maintain calcium and alkalinity in reef aquaria. But at some point, large enough water changes can do so. What volume of water change is necessary to maintain calcium and alkalinity in reef aquaria? In a tiny aquarium, 3 gallons for example, large daily water changes might be acceptable. How large is required? Figure 23 shows the drop in alkalinity for a low demand aquarium changing 0%, 5%, 10%, 15% and 30% of the water EVERY DAY. In that case, it appears to require between 10% and 30% of the total water volume to be changed every day to maintain suitable alkalinity. Figure 24 shows similar data for a higher demand aquarium (1 meq/L alkalinity per day). In this case, it takes close to a 50% water change each day to maintain suitable alkalinity. Similar data are obtained for calcium (not shown), where 30% and 50% daily water changes in a high demand aquarium (24 ppm calcium per day) stabilize at 364 and 396 ppm calcium, respectively. So, while changing 50% per day is really out of the question for any normal to large reef aquarium without an inlet directly from the ocean or a large seawater well, a 3-gallon nanoreef aquarium attached to a very slow continuous pump could maintain adequate calcium and alkalinity by replacing 1.5 gallons each day.
上节讨论了最多30%每月的常规换水对维持钙和KH没什么作用。不过，足够大量的换水可以维持。那需要多大量的换水呢？
图23显示了在一个低消耗的缸内，每天，注意是每天进行0%、5%、10%、15%和30%的换水。
图24显示了在一个高消耗的缸内（2.8dKH/天），大量换水。在这个缸里，需要每天换水大约50%才能维持相应的KH。
对于钙也是类似，这里没有给图只有数据：在高消耗的缸里（24ppm钙每天），需要每天30%和50%的换水，才能将钙分别维持在364ppm和396ppm。
很显然，对于普通鱼友来说这样的换水量是不显示的，除非有管子可以从海里直接抽水。当然，小缸是可以的。

花匠鱼

Water Changes to Deplete Something: Sulfate from a Homemade Two-Part Additive
通过换水排出元素：DIY钙镁KH补充液中的硫酸盐



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In one of the models described above (Figures 19 and 20) I showed how water changes alone cannot keep up with the demand for magnesium when using calcium chloride and sodium bicarbonate to supplement calcium and alkalinity. In such a system, I have suggested that reef aquarists who cannot find high quality magnesium chloride could manage using inexpensive Epsom salts (magnesium sulfate heptahydrate). The unfortunate drawback of using Epsom salts is the accumulation of sulfate. How well do water changes mitigate this?

Figure 25 shows the rate of accumulation of sulfate that I discussed in a previous article in an aquarium with a medium usage of the system (matching a demand of 8 ppm calcium and 0.4 meq/L of alkalinity per day). It also shows the effect of daily water changes amounting to 7.5%, 15% and 30% on a monthly basis. Clearly, the 15% and 30% changes per month mitigate the rise in sulfate over a year by a substantial amount (reducing the increase by 54% and 74%, respectively).

在上面章节里我提到了如果用碳酸氢钠和氯化镁补充KH和钙，那么普通的换水难以维持镁的浓度。在那样的系统中，我曾建议鱼友如果找不到高品质的氯化镁，可以使用较便宜的泻盐（就是硫酸镁，原文是Epson Salts 即爱普生盐，七水硫酸镁，是一种泻盐，因为硫酸镁有催泄作用。）不行的是用硫酸镁有副作用，那就是会在缸内累积硫酸根离子。是否可以通过换水来缓解？
图25显示的是，在一个我先前文章中举例的中等消耗量的缸里。硫酸盐的累计情况，钙和KH消耗量为4ppm/天和1.12dKH/天。同时也显示了在此缸中进行每月总量7.5%、15%、30%量，平均分每天换水时，硫酸盐的累计情况。很明显，每月总量15%到30%的换水很大程度可以缓解这种堆积。

花匠鱼

How to Perform Water Changes
怎样操作换水



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There are many ways to perform water changes, and some of these are outlined below.
有很多种方法换水，下面讨论一些。

Large batch water changes: These changes are what most aquarists think of as water changes - remove some aquarium water and replace it with new water. Reef aquarists often talk of changing 10-30% per month this way. These changes can be completely manual, using buckets and siphons. They can also be partially or almost completely automated. Some systems allow aquarists to open and close appropriate valves (or turn on appropriate pumps), and pumps take care of the actual removal and addition of water.

In doing batch changes, aquarists should consider the changes in the water parameters that will result, and be sure they do not excessively stress organisms. Differences in salinity and temperature are most likely to be significant, and the larger the change, the more stressful it can become for the aquarium's inhabitants. If there is substantial ammonia in the new water, as there may be in artificial salt water or possibly in natural seawater that has been stored for a while, that can also be stressful. Obviously, any organisms that become exposed to the air can also be greatly stressed. Differences in other water parameters are less likely, in my opinion, to be particularly stressful during water changes, with the possible exception of certain trace elements which may be more toxic in raw artificial seawater when not bound to organics than after they have had a chance to become bound in the aquarium or in natural seawater. The normally encountered differences in calcium, magnesium, alkalinity, nitrate, phosphate, silica, pH, etc., are unlikely to unduly stress organisms during water changes up to 30-50% using natural seawater or aerated artificial seawater, in my opinion.

大量换水：大多数鱼友都是先抽掉部分水，然后用新水补足。通常大家都会一个月换10%-30%。手动操作很容易，用虹吸法和一个水桶就行。当然也可以是半自动或者全自动换水，只要打开阀门防水，然后打开补水泵补新水。
大量的换水，鱼友首先要有数换水前后水质参数会发生的变化，以及这样程度的变化是否会导致生物紧迫。盐度和温度是很容易造成震荡的参数。还有水中是否有氨，因为人工合成盐可能会含有，即便天然海水存放了一段时间后也会产生。还有，大量换水时如果有生物露出水面，那对生物的压力也是很大的。其他水质参数的冲击我个人觉得一般倒是不会有。新水中的微量元素，因为人工合成盐中微量元素没有与有机物结合，所以可能毒性更大，这也是一个问题。其他诸如钙、镁、KH、硝酸盐、磷酸盐、硅、PH等等，如果用天然海水或者曝过气的人工合成海水换水30%-50%，应该不至于过度压迫生物，



Small batch water changes: These changes are similar to the large changes above, but are much smaller and are done more frequently. Daily changes of 0.25% to 2%, for example, can be used. One could also do a series of consecutive small water changes on the same day. This method ensures that organisms near the top of the aquarium are not exposed to the air, and that water parameter shifts are less sudden. These types of changes can be done in a variety of ways, such as by removing water via a skimmer and replacing it once a day, or by simply taking out an amount (such as a half gallon) and replacing it once a day (automatically or manually). While lots of smaller changes (say, 30 changes of 1% each) are slightly less efficient than one larger one (30% in a single batch), the difference is small (30 changes of 1% each exactly matches one 26% batch water change), and consequently other factors of convenience or stress on organisms may be more important.

In doing batch water changes of 2% or less, aquarists need not particularly worry about the changes in the water parameters that will result, as long as the new water is of reasonable quality. For example, a 1% change with new water at 55°F from a basement reservoir will change the aquarium temperature only from 81°F to 80.74°F. Differences in salinity are also unlikely to be significant.

小量换水：跟大量换水类似，不过量小，频繁许多。不同的鱼友一般每天换水0.25%到2%。而且一天可以进行多次小量换水。小量换水首先可以保证在缸高出的生物不至于露出水面，然后水质参数的变化也比较小。换水的操作有很多种，比如可以用蛋分打出一部分水，然后用新水补足；或者虹吸；或者用半自动或自动设备。虽然多次小量换水比少次大量换水效率低一些，但是差的并不多，而且，小量换水带来的操作方便，以及对生物冲击较小的影响，对鱼友也是很重要的。 在每次少于2%的换水下，水质参数的变化可以无需担心，只要新水的水质是正常的。比如，用5摄氏度的水换水1%，只会将缸水从26度降到25.79度。盐度的变化同样也会很小。

Continuous water changes: Continuous water changes, despite their name, are not necessarily performed every minute of every day. The distinguishing feature of these changes is that water is added at the same time that it is removed. The actual rate of addition can be high or low. Reef aquarists (myself included) most often perform these types of water changes with two matched pumps, one that removes the old water and one that adds the new water. Often these pumps are part of the same mechanism (such as two sets of tubing on a peristaltic pump or two heads on a diaphragm pump), but that is not a requirement. I use a dual head diaphragm pump capable of a maximum of 30 gallons per day for each head (a Reef Filler pump from Champion Lighting). In my setup, once I have a 44-gallon trash can full of new salt water, all I do to perform a 44 gallon or smaller water change is plug in the pump. The wastewater is sent down the drain. Sometimes I change 44 gallons in one shot, taking about a day and a half. Sometimes I pump for a few hours at a time, and then wait for a few days.

These changes are slightly less efficient than single batch water changes of the same total volume. A continuous water change of 30% exactly matches one batch 26% water change. As with very small batch water changes, these have the advantage of neither stressing the organisms (assuming the change is done reasonably slowly), nor altering the water level in the aquarium. The ease of doing such changes automatically also makes it far more likely that busy or lazy aquarists will actually do them.

连续换水：虽然称之为连续换水，不过并非一定是要每一天每一分钟都在换水。主要特征是放老水的同时，新水也在注入。而换水量可以大也可以小。很多鱼友包括我自己，会用两个同样的泵，一个抽水的同时一个加水。有些人用滴定泵或小离心泵来换水，我自己就是用双头蠕动泵换水的，一个缓慢的将水抽到下水道，另一个缓慢的将储水缸里的新海水抽进缸。有时候我一天换很大量，将泵开个半天；有时候运行个几小时。然后过几天之后再换。

这样的换水虽然效率比单次换水低一些，大约在87%的效率。不过对生物压迫较少，缸内水位也不会变化。对于那些懒惰的鱼友，也是个好方法，操作简单多了。

花匠鱼

Conclusion
总结



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Water changes are a good way to help control certain processes that serve to drive reef aquarium water away from its starting purity. Some things build up in certain situations (organics, certain metals, sodium, chloride, nitrate, phosphate, sulfate, etc.), and some things become depleted (calcium, magnesium, alkalinity, strontium, silica, etc.). Water changes can serve to help correct these imbalances, and in some cases may be the best way to deal with them. Water changes of 15-30% per month (whether carried out once a month, daily or continuously) have been shown in the graphs above to be useful in moderating the drift of these different seawater components from starting levels. For most reef aquaria, I recommend such changes as good aquarium husbandry. In general, the more the better, if carried out appropriately, and if the new salt water is of appropriate quality.

Calcium and alkalinity, being rapidly depleted in most reef aquaria, are not well controlled, or even significantly impacted by such small water changes. In order to maintain them with no other supplements, changes on the order of 30-50% PER DAY would be required. Nevertheless, that option may still be a good choice for very small aquaria, especially if the changes are slow and automatic.

Happy Reefing!

换水是维持水质的好方法。对于缸中产生的杂质比如有机物，重金属，多余钠，氯，硝酸盐，磷酸盐，硫酸盐，以及缸中消耗的钙，镁，KH，锶，硅，换水都能帮助平衡。而且对有些物质，换水是最好的方法。每个月换水15%-30%，无论是一次性还是分多次，本文都证实了是相当有效地。对大多数鱼友，我建议养成换水的好习惯，而且越多越好。
钙和KH，在多数海缸中都快速消耗，通过换水是无法满足的，对于这类元素，除了小缸可以考虑用换水，大缸只能通过其他办法补充。

祝大家养的愉快！