一个被忽视的问题，如何换水？（译自RC)
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：- W- k7 b( G" e6 S3 a" k7 J. s- {) N+ |
1，缸水中有什么
2，新水中有什么7 l$ G/ X0 A3 f( k8 N
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 q
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：, n* ]( N" v" R+ W7 w* C. j6 R
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
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
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：
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. 1 N; u4 G* L6 a
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。
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