I thought I had a problem with my tank because my Nitrate levels were around 15-20. I did weekly water changes and installed a protein skimmer for my 36 gallon reef tank. After many post to this website, someone suggested testing my R/O water before I added the salt. My R/O is around 10-15 ppm for Nitrates. Is there something I can buy to reduce the nitrate level in my tank and for my R/O water?