On Mon, 30 Apr 2007 13:04:19 +0100,(Carol Hague) wrote:
Fish poo breaks down into nitrites, which, if allowed to build up will
eventually kill the fish.

but it will not remain as nitrite (unless you have a badly overstocked
tank and/or bad fitration)
You of course meant to say nitrate which is the final decay product
which is not especially harmful to the fish, in contrast to nitrite.
Nitrate can only (conveniently) be got rid of by water changes, **

But I agree that water changes can be infrequent but best practice
suggests more often than once in a blue moon.

Alan is right that many fresh water trops can be kept without frequent
water changes, however, in Alan's day not many people were
keeping/breeding for example discus. That is now much more common
(easier) with modern practice.

** unless you have vast amounts of anaerobic reactors
or huge plant growth
or access to ion exchange resins at considerable cost

anyone for going to uk.rec.aquaria.misc ??