I have been running a saltwater tank for two years without a QT. I have dumped fish directly in my tank and never had a problem until recently. My tank is a community tank, no aggressive fish, all my fish are well fed and extremely healthy looking. I put in a Kole Tang that looked healthy and fed actively at the LFS. After about a week, he looked like he came down with ich. I felt like it was not big deal - I, like many of you, assumed that I always had ich in my tank and it was like a cold.
It is NOT like a cold. Since then, I lost the tang and three of my other previously healthy fish. At least three of the ones that are still alive show obvious signs of infection and I think there is little hope for them. Out of 12 fish originally, I think I will have 3-4 left after all is said and done.
There are a lot of myths surrounding ich. First of all, there are multiple strains. Secondly, a lot of what people think is ich is actually marine velvet, which seems to be more virulent. Thirdly, a fish's immunity only lasts about 6 months (according to the articles on this from reefkeeping.org).
I tried QTing fish twice before: once when I bought a fish that looked healthy in the store but when I got it home it had a sore on its side; and the second time right after I set up my tank and I bought a clownfish from petco that had ich. In both cases, the fish died. I used that as a rationale for not QTing.
I think the problem is that we do QTing wrong. A good QT tank should always be set up. We shouldn't be setting them up and taking them back down again over and over again. That, in combination with the lack of filtration that is generally mandated for QT tanks leads to really unstable tank conditions.
I am not going to make this particular mistake twice. Watching my fish die of disease is heartbreaking. They have lasted a long time with it - a testament to how healthy they were previously. I thought my mandarin was dead since I hadn't seen him in days, but I saw him last night. He has the infection so badly that his entire head is white. However, he is still fat and still swimming around. I am sure he will succumb to the disease eventually.
When I setup my QT tank, I am actually going to use both sand and rock. I know this means that if the fish is sick, it might take longer to cure the problem, but it will be worth it for the extra biological filtration. The QT tank will be set up at all time. I am not going to run a skimmer; just GAC through a phosban reaction. I'm using strip lights (since fish don't really need light) and a heater on a single stage controller to keep the temperature steady and that is it. I plan to QT all new fish for two weeks at minimum. In tank that has liverock and stable parameters, it should not affect the health of the fish adversely. All water changes will come directly from my main tank to keep the parameters as similar as possible.
Just my $0.02.
