Dear Osmio, I regret to say that I have not found your product functional. After repeated water test, it seems as though the filters are filtering very little to none of the nitrates in the water. I am getting a consistent reading of 5 parts per million. Tap water in England is typically between 5 and 10 parts per million in nitrate. This is important to me because I keep a reef tank and that is what I purchased the product for. Also I have tested other water samples in comparison, to samples from your product, so I know my test kit is functioning properly. Considering the price of both the product and the filters, which is very high, I would expect exceptional performance. I would like to return the product.