[Delphinus]

My one and only foray into QT'ing new fish was a disastrous experiment. I got scared into trying the QT for fear of introducing something like velvet into the main DT after it happened to a couple friends of mine in the last year.

Before that I had always introduced new fish straight into the DT. Some would develop ich, sometimes a couple spots would spread to other fish but in 2-3 days would be gone.

I'm left wondering if my QT tank "saved" my current inhabitants, or whether the sudden jump in bioload on the QT tank simply crashed the system and left it unable to sustain fish. The latter case is clearly the more likely I would think.

So QT'ing definitely requires a bit of caution in the setup, and definitely needs slow additions as well if there isn't already a steady state cycle in place. Ie., one fish at a time .. and perhaps some long-term inhabitants in that tank as well just to keep the cycle going. Of course this means you already have a pretty good idea that the new fish is probably already healthy. If not then maybe it needs to be passed on purchase, or go into a more hospital type setup (but that may have worse consequences, I don't know).