looks like black marbles growing on coral

Question
I have just aquired an established 55 gal salt water tank that I really know nothing about. It has black growths on the coral that look like shiney black marbles.  How do I treat this?
I also was told that is has red slime.  The sand and the coral are getting a red hue.  Should this be treated also?

Answer
Hi Kelly. The "marbles" you are seeing are most likely a form of bubble algae. Usually they are green but can be very dark green in color that they appear black. Manual removal by simply picking them off the rocks is the best way to keep this algae in check.
Red slime algae will grow in a tank that is rich in dissolved organic nutrients. Strong water flow and the use of fresh activated carbon and a good protein skimmer are a must in helping to control a cyanobacteria outbreak. Do frequent partial water changes and only use reverse osmosis or distilled water for mixing with your salt. There are plenty of chemicals out there that will rid your tank of this however what you have is actually a bacteria not an algae. If the source of the problem is not resolved it will often come back. It will also be more immune to the chemicals and harder to get rid of the next time. Use these chemicals only if you are fixing the overload of dissolved nutrients in your tank first. I have found that doing partial water changes every week of about 25-30% for a few weeks is usually enough to get your tank back into shape. You can change up to 50% at a time if you like! You need to do whatever it takes to rid your tank of the dissolved organic nutrients that has built up. Check and make sure your protein skimmer is working efficiently. If you don't have a skimmer then I would suggest you get one. If you do you should be collecting an inch or two of thick brownish greenish gunk a week. It should be thicker than water and have a slight odor to it. If you are collecting too much water than you are not collecting enough of the organic waste. Make sure you are not overfeeding either. Only feed as much as your fish will consume in three minutes and never feed more than twice a day. If the tank was moved from one location to your house then this is very common. Keep up on your cleaning and it should be gone in a few weeks!