theory on water changes


well everyone just thought id share this with everyone at fishlore everyone has told me how critical it is to do a regular 25% water change every week which I have been doing we still lose the occasional fish as I think most fish keepers do but quite a few of my friends and customers never do any water changes and very rarely lose any fish I went round to one of my mates and tested his water and all the levels were spot on and I mean spot on he assures me he has never done a water change now this baffels me so in your oppinion are water changes that critical and should you change a winning formula

thanks all


I think that how often you change the water depends largly on how long the tank has been set up and how many fish are in the tank. If your tank has been setup for a couple of years and it is a light bio load in the tank then I think that you could get away with 1 20%-25% water change a month. But a newer tank or a tank with a heavy bioload on it will need to be changed more. In the end every tank is different. If you do regular water tests and the levels are all good then you should only need to do a water change when the levels start to rise.


Yes I think regular water changes are very important As was mentioned before tank size and bioload have a lot to do with how often and how much water is changed. Most of us test for ammonia, Nitrites and Nitrates which is a good general indication of how a tank is doing, but another medium to be considered is total disolved solids(TDS). The beneficial bacteria may take care of the ammonia and turn it into less toxic Nitrites and then into Nitrates, but the feces and other waste is still there. As time goes on minerals that would be replaced by water changes are depleted. Yes the fish may survive and manage to live for a long time but without the mineral replacement and lowered TDS they most likely won't thrive and display their natural actions to the fullest.


I agree with Carol. I also want to add that it often happens that people, who have had tanks for a long time and never did any water changes (except adding water in place of the evaporated water), finally do perform a water change after which fish suddenly die. Such people are then convinced that the fish died "because of the water change." However, this is not true. The fact is that the old water contained probably a lot of nitrate; so much of it, that even a small water change could have caused a large and sudden nitrate drop in the tank, and all fish died as a result of that sudden change. High nitrate is bad for fish, but it's also unsafe to suddenly go from high to low nitrate, and vice versa. It's always best to introduce changes very gradually to any tank - be it pH or nitrate changes. If you have a very high nitrate content, it's best to perform very small but very regular water changes, to bring the nitrate down very slowly. Therefore, the "sudden death" of all the fish in this case is the result of fish not being used to low nitrate, rather than due to the water change itself.

Water changes certainly depend on the bioload (a.k.a. the number and sizes of fish in a tank). If a tank is lightly stocked, smaller and/or less frequent water changes are needed. But, nevertheless, any tank should have REGULAR water changes with gravel vacs because of TDS mentioned by Carol. An exception can be a heavily planted tank with excellent and healthy plant growth - although even most people with planted tanks perform regular water changes; only they don't perform deep gravel vacs because of plants' root systems in the substrate. In a heavily planted tank, with excellent and healthy plant growth, and light to medium stocking level, the plants themselves remove ammonia, nitrite, and nitrate from the water. And they keep the substrate clean by using the wastes as nutrients. Besides, healthy root systems also keep the substrate adequately aerated, eliminating dangerous gas pockets.

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