New to reef tanks

[Gringos]

I have been talking about wanting salt water fish for a long time. After alot of research my wife got me a 125g tank for christmas. So I proceeded to setting it up with most of the trimmings. Sump, fuge, skimmer, metal halide lighting, overflow box, live rock, base rock and ro unit. Well the tank went through the first couple of months no problems, so I added a hippo tang. He was the reason for the 125g in the first place. He has been in the tank for about 4 months now doing great (grew about an inch). Around the 3rd month came the algea problems. I now face a huge tank full of bubble algea. No sign of any other kind, just bubbles everywhere. So after alot of reading and long nights of trying to manually remove them (I can take out nets full of the stuff from the bottom), I deceided to try some crabs. I have recently gotten 6 emerald crabs. The crabs have been going at it for about a month now. I can see some rocks that I could not before but not the light at the other end of the tunnel. I have reduced feedings from 3 times a day to twice a day. What is causing these bubbles? Could it be my lighting? Please advise.