Nitrates are just a biological by product of the food -> fish -> waste -> ammonia -> nitrite -> nitrate. The problem you're having is that you are not exporting the nitrate.
If you want to reduce the build up of any product in your water (change the conditions) by changing water then you need to do large water changes. If you have 65 gallons of water in your tank and you do a 15% (10/65) water change then you will only drop the nitrate from 20 to 17 (20 - (20 * .15)). To make any change you would need to do 50% changes, which would drop you to 20 -10 = 10 - 5 = 5 - 2.5.
I use live rock / sand and a protien skimmer with no detectable trace of nitrate in my 185 gallon reef. Bit of algae on the rocks but the fish and inverts like to nipple on that.
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