Hi folks, I just had a question real quick. I bought a refurbished unit in August of 2011. Has worked great but I just had to purchase my 3rd DI cartridge this month. I am getting a rejection rate of 96.8% so I don't think it is the RO membrane. I have changed the carbon and sediment filter when I have changed the DI canister. TDS going into the unit is 288, coming out of the membrane is 9 and out of the DI is 2-4 depending on when I check. Temp is 60 and pressure is 60. The ratio of rejection is 4:1. Is this normal to go through DI cartridges this quickly?