"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?

The key design measurement for a VF is not depth but surface area. You need
to maximize your surface are in order to maximize the number of plants you
can float in it. More plants, more roots, more cleaning. A five foot deep VF
is probably no more prone to going aenerobic then an 2 foot deep one, but
over time you are more likely to clean the 2 footer then you are the 5
footer. Once signifigant mulm builds up, then you start having the aenerobic
problem. What I am saying is that it is not the depth that causes the
problem it's the depth causing you to not clean it that causes the problem.

Beside what would be the value of a 5 foot deep VF?

BV.