Cyano Bacteria (Red Slime)
From The Aquarium Wiki
What is is it?
Cyano Bacteria is a red bubbly substance (Cyanobacteria) that encrusts the rocks and glass of marine aquariums.
What causes Cyanobacteria?
While no conclusive evidence has been presented there are several factors that seem to contribute to the bloom of this pest. The first is too much proteins in the water column. The second is lack of water flow. The third is the presence of phosphates and nitrates. The final theory is high intensity poor quality lighting.
How to get rid of Cyanobacteria.
Make sure that your Protein Skimmer is adequate for the size of tank it is placed on. The skimmer companies rate their skimmers all drastically different from each other, so make sure to purchase one with a good established reputation. Try feeding less food it is possible to keep proteins down by just feeding less. Make sure that there are no dead-spots lacking water movement. Test for phosphates and nitrates. If there is a presence of phosphates make sure to run ferric oxide or a comparable product in a media bag or media reactor. If there is a presence of nitrates run some carbon in a media bag or media reactor. The carbon does not lower nitrates directly it does so by reducing the ammonia in the water column and therefore not allowing the bacteria to turn it to nitrite and then to nitrate. If the lamps in your fixture are low quality or are getting older try replacing them with a more blue lamp. Try reducing the light cycle of your tank. If your lights are on for 12 hours try reducing that to 10 or 8 until the Cyano is gone.
After all of the above have been exhausted there are some chemical treatments that have decent results. Chemiclean red slime remover, and Kent Poly-OX are two such products that should be available from any local fish store in the USA(?).
Sometimes this problem can require a vast amount of time and effort to resolve but it can be done.