It's possible that your rock has organic material inside it that is still breaking down.
I'd syphon some of your water into a five gallon bucket, take a rock out and place it in the bucket,
then use a powerhead to blast the rock. If material comes out of the rock, you may want to clean
your rocks out with this same method. I had a major nitrate problem when I first started and it
didn't matter how much water I changed, the nitrates wouldn't decrease. After a couple years, I
finally got to the point where my nitrates were zero.
Once you find out where your problem lies, chaeto should keep your nitrates in check.
Good luck
I'd syphon some of your water into a five gallon bucket, take a rock out and place it in the bucket,
then use a powerhead to blast the rock. If material comes out of the rock, you may want to clean
your rocks out with this same method. I had a major nitrate problem when I first started and it
didn't matter how much water I changed, the nitrates wouldn't decrease. After a couple years, I
finally got to the point where my nitrates were zero.
Once you find out where your problem lies, chaeto should keep your nitrates in check.
Good luck
