Well, if you think the tank is at the end of the line, with nothing to lose and with the least amount of work;
Option 1, go ahead and turn off the lights for a week. That will cause the algae to die off, then a phosphate sponge and carbon can soak up the nutrients released. After a week, return to your normal light cycle and you'll see the algae pull back in growth somewhat. Repeat the darkness for longer than a week if a week was not enough the first time around. Remember 3 weeks would be too long.
Option 2, a little more difficult, in that you need to buy some Marc Weiss "Reef bugs, its alive" which is a blend of live phytoplankton species in a resting state. Its a dry product you keep in the fridge and they hatch out in water. Cost like $20 for a ounce or 2, which lasts me 2 or 3 years. Toss in a couple of grams of this into your water every day, which will cause a phytoplankton bloom and turn the water green. If the water gets green enough, it will block light to the algae growing on the substrate and they will die off. As the nutrient's bleed into the water, the phytoplankton will bloom and get even greener. What you're going for is a green soup colored water. Your corals and filter
feeders will be feeding off of the phytoplankton, so you need to keep adding to maintain the greenish color. Once you're satisfied that whatever algae/ slime has been cleared off your rocks, you can stop the phytoplankton bloom and let the water clear up.
Option 3 and the most labor intensive, get a couple of 20 gallon Sterlite containers and mix up a batch of water, then do a 40 gallon water change, sucking out all the algae off the rocks. Repeat as needed.
No mater which option you do, you'll need to add a cleaner crew of I prefer blue legged hemit crabs to prevent algae from growing in. I personally think a tang is worth 40-60 crabs, but that's personal preference.
