Nitrate

I need some suggestions on how to get my nitrate down. Its probably coming from my water or the brand of salt i use. For about two weeks now i have been using seachem prime which says it detoxifies nitrate and i added a small pieces of nitrate blocking media to my filter. My parameters for my tank are 8.2 ph, 0 ammonia, 0 nitrite, and 40ppm nitrate. My tank has been established about 5 months. I have 3 fish 2 stars 2 emerald crabs and 2 anemone. I found a ro/di system on amazon for $50 but til i can get it is there anything i can do to get rid of the nitrate.