First off, one of the most important things you need to do when setting up a saltwater tank is of course include live rock and to place correctly ( especially if you're going to keep corals, it helps with keeping good bacteria and of course a place for fish to hide and to put corals). This is one of the major mistakes I did when starting up my tank - I didnt set up the rock correctly. I had 80# of live rock ( I got a majority of it online at a good price.. the only draw back was I could not pick the shapes) I had about 4 large (10# roughly.. and about 5-6 inches across 'round' ) base pieces that I started out with and since I had a lot of smaller odd shaped rocks, I stacked them up against the back part of the tank and on top of each other.. this left me with little room / holes inbetween the rocks.. I thought it looked ok, and it seemed to hold up the coral frags that I had well.

  Several weeks later ( after putting on the new lights) I started to have horrible green hair algae issues. I was scrubbing the rocks daily.. very very bad blankets of green hair. I purchased a HOB fuge, phosphate reactor, and started the vodka method from a suggestion ( please research this very carefully if you use it, I wouldn't recommend it for everyone - stopped shortly afer trying it) and various other things. No luck. The green hair slowly went away after dosing vodka, but then I got a massive (covering everything blanket) amt of red slime.. vacuumed like crazy to no avail.

Finally after realizing I may have bad flow I reorganized my rocks, took out some big pieces in the middle and rearranged my power heads to allow better flow. I could not believe all the deitrus that had accumulated begind those rocks! It was a big brown cloud of gunk, quite gross. I did a 50% water change followed by 10-20% weekly (instead of every two week) water changes and my algae is gone!!!

summary of what helped:
1)**open rock formation to allow good flow ( no big clumps of rocks together) ** ( this seemed to be the most important part)
2)weekly water changes of at least 10%
3)Some good power heads (# depending on your tank size)
4)Vaccuming any spots of the sand where you see deitrus accumilating ( a good open flow design will help this, too)
5)increasing amount of clean up crew members
6) use Ro/DI water for PWC and top off!!! ( very important as well)

** try changing these things before using bandaid solutions like chemicals etc - they may get rid of algae temporarily, but speaking from experience, if the problem is not fixed, it will keep coming back - plus chemicals, even though they may say they're safe for inverts etc may cause damage - research!**