George wrote:
That is true. However, few people build their ponds with an included
undergravel filter as is found in most aquariums. Most people who have a
biofilter (such as myself) build it as an enclosed structure or vessel.
Within that vessel, water is constantly being fed into it, bringing with it
oxygenated water. The sludge I was referring to occurs on the bottom of
the pond where detritus settles out and can become anoxic in areas with
little or no water flow, especially where there are rocks piled up. If
your biofilter is working properly, the nitrate and ammonia levels will
usually remain low, but the pH, over time will begin to rise because of the
build up of sludge on the bottom. That's my understanding of what happens.
It's a good argument for using sludge-loving bacteria in your pond to
prevent such build up from occurring, and also argues for increasing water
flow in areas where such build up can occur.

I can see how that works for small, decorative ponds. But what about
large ponds (say, one that is 100'x40' and 20' deep)?



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