They can be kept successfully but it is something of a crap-shoot. The anemone is going to sting anything that it comes into contact with. In a 22 gallon tank that could be quite alot depending on the size of the anemone. Once/if the aenmone settles in one place you might be able to keep softies with it as long as they are not contacting each other but that will depend on the size of the animals, the tank layout, etc. Sorry, but it's just not a straight-forward answer.