My apologies, I am sure this is covered, but I couldn't find it.   My system is pea gravel, out of cost necessity. It has worked great, I have flood/drain bell siphons. The beds are 2 feet wide by 8 feet long, and 12" deep.  I have TONS of red worms in my gravel, and they seem to be thriving. My fish (KOI) have gotten quite large, and that's great... but I have a LOT of fish poop, and so naturall…