Instead of looking for a fish to eat the algae{they will eat it if it's short..not long} look at why the algae is there. Most likely high phosphates{PO4}. Manual removal of the algae, water changes with RODI water with 0 TDS , and possibly some phosphate remover or a phosphate removing pad will go alot further in helping with the problem than a fish. It could be that the bulbs in your lighting are overdue to be replaced. It could be overstocking, not enough clean-up crew. or over-feeding. Another fish is just going to add more detritus, and add to the bio-load{problem}.