My daughter has 4 small peacocks in a 75 gallon tank which was seeded with a mature sponge. No ammonia-nitrites-nitrates after a few weeks. Since the fish are feeding and producing waste, is the volume of water enough to dissipate any toxins, sort of like a large body of water? How long will it take for the level of ammonia to rise to a level that BB start to feed and convert? Can nitrates be there but not measurable with the kits available? Fish are fine.