I bought a 75 gallon tank set up last week from someone on Craig's List. I also got a 30 gallon qt in the deal. The previous owner said that the powder blue tank had recently been bought and had ich. He had all of the fish (6) in the qt and had treated it with copper. All of the fish are doing great, but I am wondering how long I should leave the fish there before moving them back to the big tank? The big tank is running fine, the urchin, shrimp and sand sifter there are all doing well. I brought home about 35 or 40 gallons of the water that was in the tank, and filled with new once I had it set up at my home.