"GrannyGrump" wrote in message
...

It is not whether the water will change going over the waterfall, but the
action of the type of bacteria, and the waste products produced. Aerobic
digestion does not produce hydrogen sulfide or methane which smell bad
and
are toxic to the fish.

So how would a 4 or 5 foot deep veggie filter be created to not have
this happen?

Besides using an airstone, have the pump bring the water into the bottom of
the deepest part of the veg filter, and rain from near the top of the other
end. This way it helps ensure there is a good bottom to top waterflow.
Otherwise the water at the bottom of the filter tends to become stagnant.

Snooze