Posting all the peramiters you can would help but 4 main things that I know of is bad lighting, need more water changes, need a better CUC, and (If you'r not already using it) need to be using RODI water.
Knowing you'r ph, nitrate, nitrite, amonia, temp, salinity, and the age and type of lighting, as well as the age of you'r tank and a general description of what you have in it, and what kind of filtration you are using would help.