Frequency Of Water Changes

[Bugdozer]

My tank has only had a few fish in for a few days and so at the moment I'm basing my water changes mostly on the water test results. However, as a rough guide, in the future when my tank is stocked at a higher level and the cycle is properly balanced, about how often and how much should the water be changed in a 40l tank?

 

[backtotropical]

Changing about 50% of the water once or twice per week would be perfect.

You will need to change more than that just now though as it sounds like you're doing a fish-in cycle.

You should try to get some mature filter media from somewhere which will help your cycle immensely.

 

[sadguppy]

When the balance is established, once a week or once every ten days, possibly two weeks, should be enough on a moderately well stocked tank. I do about 25-35% per week, in your case this would be a bucket or a bucket and a half. Two 10l buckets if you want to be sure.

Also should add that my tanks are well planted and my nitrates don't rise too much, plus I have low nitrates from the tap. You're aiming to keep these low, so they're important considerations.

 

[Man of fish]

Right now I'm doing about 30-40% weekly- 10 days, but my tank only has 9 fish right now. Once it's fully stocked (in about a month) I'll be doing 50% weekly or even twice weekly.

 

[Bugdozer]

Thanks for the advice folks!

 

[OldMan47]

You will continue to gauge your water change frequency and size by water tests. If you add to your stock, it will mean re-establishing what it takes to keep your water good. What we suggest is that you do enough and large enough water changes that the nitrates in your tank never exceed your tap water by more than 20 ppm. If you have 20 ppm tap water, that means the water in the tank never exceeds 40 ppm for instance. What we are doing is using the nitrates, which we can easily measure, as the canary in the coal mine for chemicals that we do not measure. If you prevent a build of more than 20 ppm of nitrates, you will keep all chemicals at a reasonable level for fish health.
If you read lots of my posts you will find that I sometimes recommend huge water changes even when people tell me that their ammonia and nitrites are just fine. What I am really doing in those few cases is trying to get people to clean out chemical contaminants that we never measure. We are not able to measure all possible relevant chemicals in our tanks so I default to doing a huge water change to clean out whatever may be the problem. Although the 20 ppm nitrate is a decent enough guide, it is not totally reliable for water quality and thus the advice that I sometimes give to do added water changes when fish are having troubles.