Yesterday I took out the anacharis from my tank and dosed with Seachem Excel to try and rid my tank of BBA. Today I wake up and see the tank looking like milk so I test ammonia. To my horror its over 6 ppm. So an 80% waterchange later, I get it down to safer levels add an ion exchange resin and put the anacharis back in. Right now I've done my 4th waterchange today since the ammonia does not want to stop going up. My rainbow starts getting extremely stressed with heavy breathing so I put him in my goldfish tank (only tank I have large enough to support him) since they have similar water parameters and temperatures. I keep this tank at 77* and the Goldie tank at 75-76* (Fancy Goldfish). I try to keep him and the goldfish seperate and go to a meeting. I come home and to my horror find my beloved goldfish missing some scales and having shredded fins. The shark got out of the barracade! So the shark goes back in the toxic tank which now tests at 2 ppm :-( and I do more waterchanges. I don't have access to bio-spira right now so I try Seachem Stability which I heard works well. Some of my other fish are now showing ammonia poisoning symptoms too. Anyways this was one of the worst fish days I've ever had. Yesterday my tank is perfect and tests perfect and today, Biofilter collapse. I am assuming that the removal of the anacharis + some sort of toxicity in the excel is the cause of this. I hope to remedy the situation soon with no fish death.