Quarintine tanks are the difference between a sad loss and a disaster. It sucks to see your new babies die. But, it's even worse if they take the disease to one of your display tanks. Then you might loose everything. My books say 4 weeks if the fish was not exposed to wild fish. 6 weeks if they were. Fish diseases can be dormant or unnoticed untill it's too late. The size should be dictated by the size and behavior of the fish. Most folk don't put plants in quarintine tanks. And, if I may suggest. Use something like pepso food for the first feeding. It has always worked for me. Constipation kills lots of fish. Get them pooping first thing. Guppy might recomend skinned peas or something like that. But, Guppy probably cooks 7 course meals for their fish. BE-ELZA BUBBA DEVIL FISH