I have and Optima 4 stage RODI unit from purelyH2O. The system is probably 10 years old, but I just replaced everything in the beginning of March...the sediment filter, carbon filter, DI filter, and RO membrane. I ordered this: http://purelyh2o.com/index.php?page...tegory_id=57&option=com_virtuemart&Itemid=103 with the 1 micron option and 75gph RO membrane. I have made about 20 gallons a week...about 160 gallons total. My output TDS has just gone up to 001. My input TDS is ~155. It seems like the filters should last a lot longer than this, right? What would I need to replace to get it down to zero again? Are they subpar filters they are selling? Do you think I should contact them?