If you can give us as much information as possible, as well as the details about the problem:
size of tank, volume and dimensions
levels of ammonia and nitrite in the tank water
how long the tank has been set up
decor - do you have any live plants
water change regime - how much and how often
do you have hard water or soft water (your water provider's website may have this info, we need a number rather than words)
Answers to these questions will help us to help you.