Yes, it's the ammonia, but i liked this title better than "Growing plants with fish respiration."
You are trying to remove the solids because you have a raft system and the solids can accumulate on the roots and "suffocate" the plant. I dont remove any solids in my backyard system. I let them break down i my grow beds and let the system reuse the micronutrients. The solids accumulate in the substrate and not so much on the roots. I also have red wiggler worms in my grow beds that help break things down faster.
Theoretically you could put substrate grow beds between your fish tank and rafts and do the same thing.
brian
