Red slime algae is actually not a "true" algae at all, but classified as a cyanobacteria. Often considered to be the evolutionary link between bacteria and algae, cyanobacteria are one of the oldest forms of life on earth and date back at least 3.5 billion years. These organisms produce oxygen as a byproduct of photosynthesis, and scientists believe that if it weren't for this microscopic organism, there would be no blue skies on Earth.

Commonly referred to as "red slime" algae, the name cyanobacteria literally means "blue-green" algae. Despite the naming, only about half of these organisms are actually blue-green in color. Most forms found in saltwater are other colors, ranging from blackish green to blue-green, from orange-yellow to reddish-brown, and often appear deep purple to fully black in color. Starting out as small patches, it spreads out from there as a mat of sheeting covering.

Lighting: The use of improper bulbs, lack of maintenance, and extended lighting hours are contributors that can lead to all sorts of algae problems. While these organisms do well in the 665 to 680 nanometer (nm) wavelength range, they are quite active between the 560 and 620 nm range as well.

Solutions: Only use bulbs that are designed for aquarium use, run the lights 8 to 9 hours a day, and following the basic wattage rule of thumb, try different types of bulbs to increase the intensity and the spectral qualities of the light in the aquarium, particularly when it comes to any type of full-spectrum or color enhancing tubes being used.

Nutrients: Phosphates (PO 4 ), DOCs (Dissolved Organic Compounds), and nitrates (NO 3 ) are primary nutrient food sources for red and other slime algae.

Phosphates (PO 4 ) are commonly introduced into aquariums by means of using unfiltered fresh tap water, and through many aquarium products that may contain higher than normal concentrations of this element, such as sea salt mixes, activated carbon, KH buffers, foods, and many other sources. Also, for established reef tanks the long-term use of kalkwasser precipitates phosphates out of the water, and these phosphate based compounds can settle on and in the live rock and substrate.

Solutions: Use RO/DI filtered make-up water, a high quality sea salt mix, and be aware of the elements contained in other common aquarium products you may be using. For solutions to problems that can arise from using kalkwasser

at my walmart they have a culligan water dispenser, it's RO and UV filtered, the 5 gallon jug full costs like 13 bucks the first time then its 33 cents a gallon after that, ive been useing it for a year or so...............i will be buying a house RO/DI unit when i set up the new tank because of the volume of water i would have to haul , but for 30 gallons every couple weeks this is fine

Boss

maybe reduce feeding a bit over the coarse of the next couple of water changes and see if it helps.
also i would get a siphon happening next to it start it sucking and scrub areas with tooth brush so it goes straight out of tank. this will also slow and help eradicate the slime with out helping it spread, may need a helper for that procedure.