High nitrate only!

[Myka]

Could you take a sample to your LFS to get them to test it to confirm? 80 ppm is pretty darn high.

Btw, having high nitrate doesn't mean you should see ammonia or nitrite. High nitrate just means that there is too much nitrification going on. In a reef tank we use things like skimmers and filter socks to remove organics before they have a chance to break down and become nitrate. When you have an established nitrifying bacteria population it will consume the wastes out of the water quickly enough that ammonia and nitrite will remain undetectable.

When doing waterchanges blast rocks off with a turkey baster first, and vacuum the sand, this will help to remove detritus before it breaks down.