Nitrates

[ltjn11]

My tank has been running higher nitrates then I should have, between 20 to 50 depending on what light you look at it under. Here's my problem. My tap water is running at 20 after RO it is around 5. So after mixing it( Fluval Sea), it raises up to 10. It makes it very hard to lower nitrates when you are adding halve of what you have with a water change. Any suggestions would be wonderful. Thanks Larry