I have a Maxima, and a Crocea in my 16g nano... both clams are doing great and growing like weeds. You can keep clams under CF lights, just need to put them up as high as possible on your reef. I don't really recomend it, but I have seen it done.
As to what these other guys are saying about CA, ALK, and SG (specific gravity) I'd definatly agree with them> I know my tank evaps quite a bit of water everyday... something like 3 quarts (near a gallon). Your going to either need an auto top off, or you can do what I do, and start a Kalk drip every morning. Hope it helps
SBK