Need a reef expert....

[i have crabs]

those are pretty strong lights for almost no corals, id raise the up quite high to cut down on light the algae is gettin at least untill it gets under control, dial down the calcium reactor, excess co2 is basicly fertalizer and im betting thats the main culprit, on my ro/di unit i run 2 di cartridges so if u have a big 20" one u should be ok but maybe test the water coming out of the ro for phisphates, if u still have phosphates of anykind after the ro unit thats a problem, look into a better unit maybe or more cartridges, also get a reactor of some kind and run phosphate remover,
http://www.bulkreefsupply.com/store/...ric-oxide.html
also what do u feed? maybe ur over feeding a bit or frozen foods have high phosphate in the water there frozen in usually and should be rinsed out before adding to the tank