Hello, My tank was fishless cycled over two months then after three months of fish, biological filter was good and strong, always reading zero ammonia and nitrites. A few weeks ago I treated the tank with Tetra Life Guard which may have compromised the bio filter. After treatment I did large water change and added carbon back to filtration. Past few weeks the tank was reading .25-.5 ppm ammonia, zero nitrites, but increasing nitrates. It seems that the ammonia processing was slowed, but nitrates were still processing. I have been doing twice a week water changes (30 and 50%), and adding Prime daily to deal with residual ammonia. Today the water is white cloudy, but bio processing has been picking up, ammonia is 0-.1, and nitrites are zero. I understand that this is a bacterial bloom, but I thought this was a symptom of compromised bio filter. Why didnt this happen two weeks ago, and only now seems to be happening once bio filter kicked back in? Ammonia and nitrites are zero, but is there anything else in the water that would be toxic to the fish during a bacterial bloom? I havent tested nitrates because I'm running low on the solution, but I suspect they are <5ppm given the frequent large water changes. KH =5 GH= 7, PH = 8 75* 29g planted Also, I have a cycled sponge in a QT that is processing ammonia daily. Would it be wise to add this to the main tank?