algae taking over

I currently have about 20 (3 Nassarius snails, 1 turbo, 9 astrea, 2 cerith, and 6 nerites) , a emerald crab, 3 hermit crabs, and two sand sifting gobys but the algae is still outrageous and I also have a protein skimmer on it and its a 20 gallon tank running a kessil a150w ocean blue light . So...