If the algae you are refering to is slimy to the touch and when scraped off after a couple of days it comes off in sheets then it is probably "Red Slime Algae", and is actually not an algae at all but a cyanobacteria.
Some things that cause the cyanobacteria to grow are high phosphates, high nitrates, incorrect lighting, and a high level of dissolved organic matter.
Cyanobacteria like conditions of low light and low current flow. Changing the bulbs if it has been a while and increasing the current flow can help reduce a cyanobacteria problem.
Because cyanobacteria is a bacteria there are anti biotics on the market that will kill the bacteria but it will also kill some of the benificial bacteria and it is always better to find the source of the problem anyways.
Some ways to rid yourself of the pest is to first syphon as much out as you can.
Use only high quality water for top off and water changes. RO water for example.
Use only a high quality salt mix that does not contain phosphates.
Keep the protien skimmer clean if you have one.
Change your bulbs if it has been a while.
And regular water changes. Maybe a few a week to help rid any excess nutrients that may be present.
