The stock lighting on the cubes isn't strong enough to keep anemones. These are some of the most difficult creatures to keep in the hobby, and shouldn't be attempted until you're very clear on they're needs and then only in a mature tank that's been setup and stable for close to a year.
Clownfish don't need an anemone. In the wild they use it as a safe haven. In our aquariums they don't need it, because there aren't predators looking to make a snack out of them. At least if you've setup a tank correctly there shouldn't be. :lol:
My clowns have hosted things besides anemones. Frogspawn, Torch, mushrooms, Green star polyps, pink paly polyps, Anthelia, and my favorite was a tank-raised occellaris that really took a shine to the cleaning magnet. :mrgreen:
Bottom line is your tank,as it is, isn't suitable for an anemone. Your clowns will do just fine without one. If you decide you really want to try to keep one, do some research on them, upgrade your lighting, and wait until your tank has had time to 'mature'.
Good luck,
B