It sounds exactly like red cyanobacteria. It is not an algae, it is a bacteria. Cyano is a combination of a nutrient problem and water flow in that area. It is easy to say don't feed as much and increase water flow in that area. However, I have done that myself and sometimes it still rears its ugly head. The best stuff I have used to combat the problem is called Chemiclean. It doesn't affect anything else, just the red cyano. All of you corals, fish, inverts are totally safe, I have never lost a thing using it. You need to follow the directions to the letter, stop skimming for 48 hours, remove carbon, 25% waterchange after 48 hours, etc., etc. I have found that it takes about 3 water changes before the skimming returns to normal. One after 48 hours, another 25% a week later and another 25% a week later after the second. Sometimes, it will stop after the second, but never the first, in my experience. It is called Boyd's Chemiclean and you should be able to get this at any LFS or online store.