Slight problem with nitrates

[tuwhada]

So I have this 20xh tank. That I have had up and running for a few months. It does have some corals some inverts and just a few fish in it. Not even close to being over stocked at all. I did overfeed alittle b/c I was trying to figure out how to feed my sun polyps but I ensured that I did regular water changes of anywhere between 10-20% (and I do gravel washes).
So my nitrates seem to stay at around 40, which is borderline for being bad. I have another tank that also has a nitrate level of 40 but that is fish only so it never really concerned me. This tank concerns me. Today I did a 20% and I just tested the water and it is still at 40. Why is it not going down after my water changes is there anything I can do. Oh the filtration is one of those eclipse hoods.

Thanks
Christina

[malkore]

water source: tap or R/O?
if tap water, test it for nitrates.

how old is your test kit? anything over a year old shouldn't be trusted on a saltwater tank, and should be replaced.

[phases99]

What type of filtration are you using? If you are depending on anything but LR and/or LS for you biological filtration you will always be battling nitrates as they can not do denitrification.