Hey what's up? Some things that will help diagnose. What are your water perimeters? Do you test your phosphates? Do you use ro water? Is your tank in any direct or indirect sunlight?
list everything from a - z including what sirreefalot said.
Size of tank
-Livestock in tank
-Water change schedule and size
-Are you running a phosban and carbon reactor
-Do you have a good clean up crew
-What are your nitrates
-What lights are you using
-How much and many times a day do you feed.
-What do you feed the tank
-Are you running a skimmer
-Do you have a fugue
-What flow do you have in your tank
just a few questions to get to the answer you need