Need some advise. I bought 2 fish from LFS put them in my QT and they both died. Both had what I think was fin rot and I wasn't able to treat. Thank God for a change I didn't put them directly into my DT.. Slowly learning! Anyhow, do I have to treat the QT before I buy any more fish? All I have in the tank is a bunch of PVC pipe with a canister filter and sponge filter (Bio)