Hi and welcome unplugged_55!
We need to ask you some questions about the tank before we can help you with this.
1. How long has the tank been running?
2. How often do you perform water changes and how much water do you change at a time? How often do you gravel vac?
3. How big are the fish and how often do you feed?
4. What chemicals do you add to the water (ie- water conditioner, ferts, etc)?
5. What is the temp of the tank?
6. Do you have test kits for ammonia, nitrite and nitrate? If so, can you post the results?
7. Is the water a cloudy white or does it a have a greenish tint to it?
Bryan