It certainly sounds like cyano
. That is an issue of nutrients going in to the tank, and not enough coming out. There are chemical additives that will kill the cyano
and remove it, but that wont get rid of the nutrients in the bacteria, or more importantly, it does NOTHING for the underlying cause.
The first likely cause is excessive feeding.
Next, is inadequate nutrient removal. Freshwater style HOB
filters or canister filters are often not up to the task of cleaning salt water aquarium. Upgrading the filtration to a skimmer is often the first step on the road to nutrient balancing.