Carpets need more space than 4 gallons. I was foolish to want to keep a smaller one, about 3 inches in a 20+20 until I could upgrade but I never was able find a healthy anemome, luckly me. They can be very difficult even in larger tanks. Maybe sperry's Stichodactyla tapetum would work but I still would not try it in a 4 gal since lighting could heat things up too much. But hey, it is an excuse for a bigger tank right?