You need tests and need to know the parameters. Coral foods, such as reef roids, can really increase the nutrients in the water, causing algae if your not careful, especially in a small 15 gallon tank, the water quality is more delicate.
I will sometimes put a pinch of reef roids in with my frozen food mixture. I feed raw foods so they provide the aminos that corals need. However I do notice the corals looking happy after using reef roids. If you decide to use a product similar try to limit it to once or twice a week. Over using these products will cause more harm than good in your tank chemistry.