07-16-2009, 08:44 AM
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Originally Posted by mattsilkwood
ok im asking about a 90 gal, its got a rena xp3 filter, and it will be stocked with tropical fish fairly heavy.
then i have a 30 gal with a hob filter, stocked with goldfish and catfish, not very heavily.
the 30 gal will eventually be used as a breeding tank for snails and shrimp and im going to get either a 55 gal or a 75 gal for goldfish, channel catfish, and bluegill.
I have a 115g with the same filter, and a 90g and 70g both with an Eheim Pro2. I do a 40-50% partial water change every week, never fail. I agree with 1077, a 25% pwc every week is the absolute minimum. As you, like me, have heavily stocked tanks, more water is better. But less water more often is preferable to more water less often, so get in the habit of doing once a week. Your fish will thank you, and so with the plants if you have any.
The reason for the pwc is biological. Fish produce urine and excrement, and while a filter will remove the solid waste from the water column it cannot remove the liquid which remains in the water until you remove it with a pwc. The solid waste gets trapped in the filter and there it breaks down into liquid. No filter can remove this. The pwc also removes some of the nitrates, which is not so critical in a heavily planted tank because plants require nitrate, as does the anaerobic bacteria in the substrate, but there is still plenty even with a 50% pwc.
An interesting observation: the book that came with my Rena filter suggests a pwc once a month, at which time the filter should be cleaned. Nonsense. In a thickly-planted tank with a smaller fish load, you could manage with no pwc; many aquarists do this. But most of us keep more fish than this regime will accomodate and a pwc of 25% minimum but preferably 30-40% will maintain a much healthier system. Of course, with larger fish more frequent water changes are necessary due to the increase on the bioload from large fish.