Newbie 75 gallon

[gregzz4]

I went through something similar back in 2012 when I started my tank with mostly dry rock. Although mine wasn't nearly as bad as your's, I was able to clean it all out in the tank.
I had a canister filter available so installed it on the front of the tank and scrubbed everything with a nylon nail brush. I used a turkey baster to flush the rocks during this process until nothing came off the rocks.
Worked very well for me and pretty much removed all the algae.