RO/DI filters question

[rsarvis]

I have an airwaterice.com RO/DI system. I'm changing out the filters and it appears that it came with the water going from the 1micron filter > 5 micron > 10 micron. I would have thought it should go 10 > 5 > 1, weeding out the biggest stuff, then the medium size stuff, then the small stuff. Is that wrong? Or am I right and it came wrong? If I'm right, that would explain why only the 1micron filter looks really dirty?

 

Anyway, also, how do you all know when to change the RO membrane and DI thingy? If my TDS is rising (used to be 0, now it's around 4), does that point to something in particular needing replacement?

[Chad]

You are right, the biggest (and most common particle size) first then progressively smaller. Otherwise, the larger filters are useless (the small one filters everything and fouls faster).

 

Most RO membranes are in the 97-99% efficient range (meaning that 1-3% TDS are left after the membrane). The DI is the part that finishes the work. If the membrane is more than a year or two, I would replace it, but otherwise I would just replace the DI media. IME the DI and carbon filters last 1/2-1/3 the time the membrane lasts.

Edited April 30, 2010 by Chad

[Coral Hind]

I wish I got a 1/2 to 1/3 ratio from my DI filters. I have a zero TDS reading coming out of my RO yet I still don't get that kind of ratio.

[Chad]

I suppose how my RO/DI fares with DC water has yet to be put to the time test... I did just completely overhaul it a couple of months ago (it was definitely due)...