H. Crispa and H. Malu can be kept healthy and happy virtually forever. The real issue is getting one healthy and happy in your tank. They do not travel well and most you see for sale are not in good shape at all, even at reputable stores. If you get one in your tank and it is still growing and healthy after 6 months you are usually in good shape. However, anemones can die very slowly, and sometimes an anemone can hang on for months before finally giving up. That's where the "hard to keep over 6 months" comes from.