Do you know where your at in your cycle? The comment above is correct but a pretty blanket answer. You need to check your parameters. If something is out of whack or too high then you may need to take action. To say do a water change when your cycled doesn't really answer the question IMO
Check your parameters and post the numbers up so we can tell where in the cycle your at. Also what are you using for an ammonia source?
"When creating an aqua scape, strive for the beauty of imperfection, as its art and there is no wrong or right, it's left open for interpretation" James Findley