You can put it in your skimmer area preferably. Leave it there for at least a few weeks. In the future, have two sponges.... One for the QT and one in your sump. That way you just switch them back and forth. But, when you take it out of QT, rinse it out and let it dry out for a day or two before putting it back into your sump (safety precaution). You should always keep one in your sump too for emergencies.