[Roland S]

hi

as the title says how do you tell if its your resin or ro filter that needs changing when the ppm starts to rise?

[Spruce]

Simply by taking a tds reading before and after the membrane. The r/o membrane should be around 97 - 99% efficient. In other words a tds of 100 in should come out the pure side between 1 and 3 depending on membrane, water pressure etc.

Anything higher than that will use resin quicker to polish off, so you have to balance the cost between replacing membranes and replacing resin.

[Roland S]

Thanks spruce that's really helpful. I'll fit a drain off tap and do as you suggest.

Thanks again

[Spruce]

What r/o have you got?

you also need to take a sample of water from the r/o after the r/o has been processing water for about 5 minutes.

It easy to get an input tds reading as you just get that at the tap the r/o is connected to.

We had a 450gpd RoMan type r/o. It was one that had the third filter housing as a resin filter. The pipes were all connected together with John Guest couplings. Firstly, we unplugged the pipe from the pure outlets of the membranes to the resin filter. We then fitted another length of pipe into that fitting, diverting the water into a bucket. Once it had run for a while, we grabbed a sample from the running water and tested it with our tds meter.

We now have a 4040 and have made this problem easy by fitting an inline tds meter. Now with the press of a button we can read the r/o output before the di and then the output after di. The tds starts off very high when the r/o first starts but settles down to a 98 -99% efficiency within a couple of minutes.

[Roland S]

the whole system i bought with the van, its a "k systems". i think rigging up an inline tds is the answer like you suggest. all my plumbing is in 1/2" hose pipe so i've just got to track down some fittings to make up some t peices that will take the hosepipe and the 1/4" push fit.

thanks again for your help