Hey thanks for all the positive comments all, and the link! I'd like to try the Mg thing but I have to wait till I go to town to get a Mg test kit. I love the way some of the macro algae looks (the violet/purple gracileria I think) but it's a constant battle. I should go caulerpa hunting tonight.... The sea hare seems to be munching away.
as to the person who asked about a derasa in a 55. I don't see why not, at least for a while, they DO grow HUGE (I think 18" or more) but that will probably take a bit of time so you could have it for a while in your tank provided you have enough light (MH or T5HO) and your tank is mature/stable. I plan on having to say goodbye to mine when it outgrows the tank or (likely) getting a larger system (Drew wants a 180 but would rather go FOWLR on that one so in that case the clam will have to go)
PS: here is a pic of the algae in question...I can't ever seem to get a great pic of it, it's like a ninja
