[Paul erithwc]

At what tds reading would you change your 40/40 ro ?

Thanks  Paul

[martin hulstone]

I change at 40-50

[Paul erithwc]

Mine is at 60-70 out the ro and 360 before the ro

[Ian Lancaster]

Mine is at 60-70 out the ro and 360 before the ro

If the RO is working effectively the product maximum TDS from an input of 360 should be 18 (95%).  You should get better than this from a new membrane, depending on input pressure.  When the TDS rises to 36 (90%) the membrane is on its way out, or there's a fault in the plumbing somewhere.

[slap bash]

I did some research on a few USA sites and they say when a RO is unable to reduce the taps TDS to at least 10%  of the sample water its stuffed. So if your TDS is 320 like mine, it should reduce to 32 TDS or less then your Di become  uneconomical on resin. I would think its a guide.