Richard Sexton wrote:

Why don't yopuu pond folks just infuse fresh water at a constant
but slow rate nd let the overflow bleed off? That's what poeple
with 100+ aquariums do. Then you barley need a filter.

Ever notice pics of discus breeders tanks that MUSt have the cleanest
water possible? They have like 1 sponge filter in a 60 gal tank. What
you don't see is the overflow and continuous water gong into it.

Some people do. One of the biggest problems is raccoons. I lost count of
the number of people on this group who've had automatic top-up systems
ruined by coons - with a resulting massive influx of chlorinated water.

The other thing is that people with 100+ 15 gallon aquariums are
obsessive :-) They don't really care about the cost. Someone with a
1500gallon pond, otoh, is just small-time, and with the cost of metered
water in some places an adequate replacement rate (at least 400g/wk) seems
like a lot.
--
derek