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What’s With Water Changes?

Posted on Sunday, November 8th, 2009 at 9:16 am by

One of the most basic aspects of maintaining a reef tank, is performing water changes. In this article we will cover various aspects regarding the importance of water changes, as well as why and how often they should be performed.

Why Should I Do Water Change?
This is a common question amongst beginning reef hobbyists.  The most immediate answer is that water changes facilitate a manual export of nutrients from the water column.  In this particular case, nutrients refers primarily to nitrates, nitrites and phosphates. These will be discussed in much more detail in another article, but let’s highlight for now that these compounds, at high levels, will be detrimental to the health of your reef, as well as promote the growth of nuisance algae. And although we have other methods removing nutrients from our reef systems (protein skimmers, GFO, biological filtration,  etc), many advanced hobbyists agree that these methods should supplement water changes, rather than replace them. In addition to removing nutrients from the water column, water changes provide an opportunity to remove detritus that has settled in areas with insufficient flow, as well as assist in the manual removal of nuisance algae. Lastly, water changes replenish many important trace elements that are used by your reef inhabitants.

How Much Water Should I Change?
We convinced you that you should do water changes, the next question is when, and how much.  Let’s begin by saying that all we can really do is make recommendations. There is no substitute to watching your reef and responding appropriately to it’s needs. There are many elements that contribute to the how much and how often question. If water changes are used to remove nutrients from the water column, then let’s look at variables that increase as well as decrease these compounds in the reef tank. You can begin by looking at your livestock. Biological waste from the animals  in your tank coupled with feeding practices are the main contributors to increased levels of nitrates, nitrites and phosphates. Therefore, as the number of fish increase within a given tank, more food is used to feed them, and in return, more waste is introduced to the tank. We also need to take into account other methods of waste removal such as protein skimming, chemical removal, and biological filtration.

In most reef aquariums, it is recommended that 5-20% of the water volume is changed every month, with smaller, weekly changes preferred over larger monthly ones.  Again, this is only a recommendation, as there may be instances where larger quantities must be changes.

How Should I Do a Water Change?
I can just hear someone saying “ummm….take some water out and then add new water back in….?”. And while, yes, that is in essence what we are doing, let’s look at it in a little more detail. Let’s pretend that we are doing a 10 gallon water change on our tank. Make sure that you pre-mixed 10 gallons of saltwater, and that the Specific Gravity of the new water matches that of your reef tank.  I personally like to let to solution mix for 24 hours before doing a water change. That insures that the salt mix that I use has completely dissolved in the water.

Rather than simply siphoning 10 gallons from the top of the tank or sump, we recommend that you use a hose and try to reach into corners of your tank and sump. Try to get into areas that may not have optimal flow, and where detritus or uneaten food may have settled.  This intentionally targets areas that are likely to cause problems in the long run.  Once you have siphoned out 10 gallons of water, simply pump or pour the new saltwater into your system, and you’re done.

In summery, we recommend that you :

  • pre-mix your new batch of saltwater for at least a 24 hours, and ensure that it is of the same specific gravity as your tank.
  • perform a 5-20% each month, preferrably in smaller, weekly increments
  • make sure that you siphon out dead zones (areas with little flow)

We hope this has been a helpful article, please let us know if you have any questions.

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