i have a 55 gallon that i set up about 6 months ago i have a pleco, blood parrot, and a jack dempsey. i tried introducing a new tiger oscar and he died this is the third time this has happend my water readings are fine, i checked. i think it has something to do between the pet store and the release. from the pet stroe to the house it is about an hour but the pet stores say thats enough time. it seems that everytime as soon as i release the fish they start acting weird then starting floating around life less then in the next day or two they are dead. i think i am doing everything right i float the bag for fifteen minutes for them to adjust then i let them out and it goes down hill from there. maybe you guys have different methods that you could share.