I have a pair of pepermints in my 29g. They are very personable. They come out and beg for food whenever I'm working in the tank. They'll even come and crawl over my hands and 'clean' them. When I want to target feed just them I'll pinch a bit of flake between my fingers and let them come up and pick it out. They are little hogs. I'm always suprised by how much such a little critter will eat. My biggest compalint is that they are always stealing food from my corals. I have to make sure they are well feed 1st otherwise they will go around the tank raiding all the polyps.
I know these guys will canabalize eachother if you have too many in one tank, especially if some are smaller than others. I'm not sure how many is too many though. Probably depends on the tank, how many hiding spots it has, how much you feed, etc.
Mine dissapear for a couple of days when they molt. You think in a 29g I could find them but they are excellent at hinding when they want to. Mine seem to produce a brood about every two weeks and then molt within a day or two.
Word of caution I've seen some places that call all red and white shrimp pepermint. If you want them to eat aiptesia make sure you're getting true pepermints. They generally are not quite as bright as other red shrimp and are clear with red stripes. The camel which is often called a pepermint is red and white striped (not red and clear).
Oh and no I've never heard of them eating zoas.
