I was doing some reading on prefilters (ran across a few of your posts across the interwebz Russ) and had a few questions.

I purchased my 3-stage kit from BFS in Dec 2011. I am still using the original sediment, carbon, and RO membrane that came with the kit. My DI has been changed a hand full of times. I have a dual meter reading after RO and after DI. After RO, my readings get down to 8-10. After DI, they are 0.

I am trying to determine when I need to replace the prefilters. I was under the impression the sediment filter should be changed when it gets dark, mine has yet to change colors. The carbon block is rated at 20,000 gallons, which is way more than I have made. I estimate at most I make about 2000 gallons a year, so being generous on that estimate I have made maybe 5000 gallons over the last 2 years. I have not noticed any drop in rejection from my membrane and the pressure is still kicking around 70PSI.

Additionally, I was thinking of adding a 4th stage for the Chloroguard Chloramine block. First off, does this cartridge fit in a 10" housing? Secondly, if added, where should this be added to the system? After sediment or after the regular carbon block? If I add the chloramine stage I'll probably just replace the sediment as they are cheap, but just curious what I should realistically be doing.

Thanks in advance.