Been an aquarist for some years and have never had an issue with high nitrates-(Readings in the 80's) I Have 2 20 gallon tanks-Lightly planted not overstocked- 30% + WC weekly-0 nitrates in the water supply-I use both undegravel and hang on filters-I thoroughly vacuum the gravel with each WC-I'm at a loss! Thanks for reading!
Have you tested the water straight out of the tap to get a feel for the possible basis of the issue?
Changed /added foods in the last couple months? Removed / done a big cut of stems plants /live plants?
Is your tank cycled and have you changed / removed an old filter pad or changed filter lately? If you have washed a filter pad in chlorinated tap water you may have killed off a bunch or all of the beneficial bacteria (BB).
New to FW fish? First tank in a long time or EVER??? Need some info on keeping fish?
No measurable nitrates in the water supply-No changes to food-I rinse the filter media in removed tank water-These tanks are approximately 2 years old and have normal levels of ammonia and nitrates-I haven't made any changes to the plants-