I have 125 gallon fish tank. I had a thriving tank that was doing very very well. My water quality was nigh on perfect. I did notice I had about a 20 PPM nitrate. I read some articles that said that amoquel was great for detoxifying the nitrate. The instructions are very specific. It said to add 1 oz per 60 gallons. I added 2 oz and followed the rest of the instructions. My 02 at the time was at 8.0. I lost half my fish that night. Over $800 in losses. I'm hesitant to use it again but I keep seeing people say they're having great success with it.