What reading do you get?
You might have a lot of gunk built up in the gravel. How old is the tank? Try vacuuming it with a gravel vac syphon.
Are you also feeding too much perhaps? Ammonia -> Nitrites -> Nitrates. Too much ammonia sources will generate more nitrates.
Also, what water are you using? Tap? Try testing your tap water for nitrates. That could be a source of the nitrates.
Hi I'm new to keeping shrimp and I need some help with my nitrate levels
I have bought a de nitrate to put into my filter, duckweed for the tank, and am using distilled water, but my nitrate levels are still really high.
5 to 6 shrimp including 2 pregnant shrimp died last week, on average of 1 to 2 shrimp daily. The shrimp seems to be doing alright the past 2 or 3 days and no deaths so far but when i do the tests, the nitrate levels are still high.
Anyone have any idea why?