Do you think 20G will be enough or if I really want to keep the angelfish will I need something even bigger, say, a 40G? When I called the pet store yesterday she said that angels will get as big as your hand and if I do a 20G when they get bigger I'll have the same problem all over again. I really wanted to ask why she let me buy the 2 angelfish when she new I was also buying a 10G... So, 20G or 40?