Red slime algae tends to build up in saltwater aquariums and is composed of cyanobacteria. Two factors can affect the algae buildup in your tank: the amount of light and the amount of floating organic particles off which the algae feeds. There is no single step you can take to eliminate red slime algae from your saltwater tank, but there are several steps that, when combined, will remove and reduce the algae buildup.
Scrape any algae off the walls using a razor blade. If the tank is made of acrylic, use something plastic --- like a credit card --- so you don't scratch it. Collect any of the free-floating algae you scrape off with a fish net and dispose of it.
Vacuum red algae off the gravel rocks at the bottom of the tank with a gravel vacuum. These vacuums create a siphon of water that is strong enough to suck up the algae particles but not the gravel. Follow the manufacturer's instructions.
Perform a one-quarter water change. The water you exchange must meet the same parameters as the water currently in the tank (same pH and salinity). A water change will remove many organic compounds that promote the growth of the bacteria that spreads the algae.
Remove any unnecessary lighting from the tank. Corals need a specific type of lighting that will vary depending on the corals in your tank. Remove extraneous lights --- especially sunlight --- as this promotes the spread of the algae.
Introduce algae-eating inhabitants to your tank. Certain crabs and blennies are known for eating the algae.
Tips & Warnings
- Feed your fish less food. Overfeeding adds organic compounds to the water, which is one of the primary causes of algal spread.
- Add a protein skimmer if you haven't already (though if it is a reef tank, it should already have one). Skimmers remove phosphates and other compounds that contribute to algae growth.
- Changing more than one-quarter of the water at once can shock your fish, especially in a reef tank with coral.