Re: Film on surface
> A recent thread on alt.aquaria discussed a film forming on top of the water
> after a while. One answer suggested that this was a protein film of oils etc
> from waste food and from the keeper dippng his hand into the tank. The other
> suggestion was that this was in fact a precipitate of calciunm carbonate. The
It's organic, most likely. Calcium carbonate (CaCO2) disolves in water
normally and even if it didn't it would precipitate out (going to the
bottom), not the surface. The film in this case could be dust from the
air or some sort of microscopic life living at the surface of the water.
Frequent water changes should get rid of it.