11-08-2009, 08:09 PM
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We all seem to be on much the same path with this, but I would like to share some observations arising from my reading of a good article in the November 2009 issue of TFH on this subject.
I have frequently commented that changing less water more often is preferable to more water less often, and I think that is still true if one is considering a partial water change weekly rather than bi-weekly or monthly. But the data in the referenced article sheds some different light on just how much water should be changed. I won't repeat all the data, but the conclusion is that changing 50% of the tank volume once a week has a significantly greater benefit on the fish than changing 10% every day of the week.
The reason is that the toxins in the water, pollution we can call it, build up significantly every day, and only removing a small percentage daily means that the toxins are increasing far more as each day goes by; in other words, each day there is a high percentage of pollution in the aquarium. In contrast, changing 50% once a week is cutting the pollution in half, with the result that day by day the pollution will gradually increase toward the end of the week; in other words, the fish are only going to be subjected to very high levels of pollution at the end of the week just before the 50% water change, so during the previous days they are exposed to slightly less pollution that they are with a daily 10% water change. OF course, changing 50% or more each day would be ideal. But most hobbyists can find it easier to maintain a regular weekly schedule rather than a daily one.
Water stability is usually cited as the reason for regular but smaller water changes. This may be true for water parameters like pH and nitrates, but there is no logic in maintaining more stable pollution in a tank. No one could logically dispute that reducing pollution is a benefit and the more the better. At the same time, a significant weekly water change will actually work to maintain more stability long term in the water parameters.
I have been changing 40-50% of my tanks' volume every week for more than 15 years without really understanding the added benefits. It is worth understanding why something works, but the fact that it does work is obvious whether or not we understand the reason.
Last edited by Byron; 11-08-2009 at 08:12 PM..