your tap or rain water has heavy metals?
The parasites and bacteria are ON the fish, not usually free in the water.
up here in the frozen wasteland one DOES NOT open the windows all fall, winter and
spring. instead we use air exchangers. a veggie filter is like an air exchanger and
the surface of the water exchanges gases.

I think more fish die each year from people forgetting that the water is running than
in ponds with a veggie filter. Ingrid

On Mon, 14 Apr 2008 20:04:00 EDT, ~ jan wrote:
In my case though, doing a water change
decreases heavy metals and can reduce parasites & bacteria, imo.

When I first got into ponding one of the senior club members compared not
changing one's pond water to staying in a room without opening the windows
now and again. Or imagine having your car on recir. air after you've just
taken the family out for a Mexican dinner. eg ~ jan