What is it and how do i get rid of thie Alge

I'm going to bet you have high nitrates and phosphates that are fueling the algae growth. Lighting may also be a factor. Whats your lighting set-up and how old are the bulbs?
Siphon out as much as you can, do fairly large and frequent water changes, go lights out for a few days, cut way back on feedings, run GFO or another phosphate remover. Its probably going to be a battle, but it can be beat. If you haven't looked at them an algae scrubber might be something to consider for a long term solution to nutrient control.

 

Are you using RO/DI water? I would scrub the rock, do the water change, then go completely lights out for a few days. Try to limit ambient sun light and everything. Also are you running any type of phosphate removing media? GFO, phosban, anything like that? It may be a good idea to look into something like that.

 

To me, those bubbles are a dead giveaway that it's dinos. If you had cyano and nuked it and now these, what you did was dump the nutrients from the cyano back into the water and these took over. It's a PITA but take an airline hose and suck them out. That will buy you a few days before they come back. Then the standard suggestions apply like GFO and carbon (high quality, of course) and cutting back feedings, etc, and also keeping your pH up. I read a reefkeeping article that said you want to keep it at 8.4 and overnight is especially important.

As far as cutting your lights back, I have a differing opinion that is not common. Cease your feeding, but keep your lights on. Or feed only right before lights out every other day, and only enough for the fish to mow down quickly. This will cause the symbiotic zooxanthellae on the corals to soak up the nutrients and feed them to the corals. This is what I did but I was also running a scrubber. Surface skimming is especially important so make sure that's on par.

Blacking out the tank will kill off the algae, but the blackout has to be 100% and for several days. This is 1) stressful on your fish/corals 2) not natural 3) causes all the nutrients in the algae to get released into the water column, where it must then be filtered out. So for that method you would need skimmer, filter socks/pads, GFO, Carbon, water changes, and the patience to not turn your lights on for days.

But either way, sucking that crud out is step #1. If you want to do it as part of a WC, then that's good. Use a small siphon hose and if you have a valve on it, crank it down so that you're getting just enough flow so that you can suck right onto the rocks and pull the gooey stuff off. It will take time so slow flow is the key unless you want to do a massive WC. I used airline tubing and went thought the whole tank and only pulled out a few gallons, you can easily cinch the airline tubing while you're searching for areas you missed. Also you can buy various diameters of flex vinyl hose at any HWS if that helps.

Good luck