hey if its a 4X55watt, you should be able to keep in fact most clam species although it is better if you keep low light demanding clams such as squamosa or derasa. But if you place crocea or even maxima up high, you should be able to keep them, but IMO for maxima or croceas go for MH. In fact some high grade maxima need >250watt to thrive. Bad point abt PL is that they get dim very slowly and to us there wun be much difference but to your inverts they are lots of difference and they will not thrive as well as before and in fact some will bleach and by the time you notice it, it will be too late.