RO/DI

GaZZaW · Jul 8, 2018

Good morning all,

I have an ro/di unit with a triple inline tds meter, you know the one with the tiny display.
I had some cash burning a hole in my pocket so i got a HM digital COM-100 ec/tds meter.
Measuring the ro/di shows 1.3 TDS on the com-100.
question is, do i need to replace the membrane or filters or di resin? which ones deplete first?

Dr. Reef · Jul 8, 2018

1.3 tds at what stage? if its after membrane and before DI, its not a problem but if 1.3 is after DI then its time to either replace membrane or DI depending which one is depleted.

GaZZaW · Jul 8, 2018

after DI, collected water. thanks.

Dr. Reef · Jul 8, 2018

what tds after membrane and before DI

GaZZaW · Jul 8, 2018

after membrane its 2 tds on inline meter.

Dr. Reef · Jul 8, 2018

so if its 2 tds after membrane and going into DI and after DI is 1.3 tds then it means DI is exhausted

GaZZaW · Jul 8, 2018

ok thanks, so 2 after membrane is ok? should i leave membrane till it rises or after a certain amount of time in use?

Dr. Reef · Jul 8, 2018

yah generally 5-10% of the TDS from tap going in.
i have a 150-180 tap so about 7-10 tds. i usually change every 2-3 yrs (mostly 3) or when tds run steady at 5-8 after membrane. DI will catch the rest and run it down to 0 but DI will exhaust very fast.
Let unit run for atleast 1 hrs before checking for tds at all stages.

GaZZaW · Jul 8, 2018

great info, thanks very much.

Dr. Reef · Jul 8, 2018

your welcome happy reefing.

redfishbluefish · Jul 8, 2018

As long as the TDS coming out of the membrane is still low, and flow hasn't change, your membrane is just fine. I'm over ten years on my membrane and still running at about 98% rejection. Note that I flush my membrane after ever water run.

However, what needs to be changed with some frequency is the DI resin, indicated when TDS after the resin is no longer zero.

In addition, the "pre filters"....that is, sediment and however many carbon blocks you have....need to be changed on a regular basis. For me, it's once a year, but that will depend on the amount of water you make, and how "dirty" you're water is. If your unit has a pressure gauge, that will indicate when the sediment filter is starting to clog.

Here's a video from BRS that will explain filter changes.

One more thing.....to extend the DI resin, I run the first five minutes of start-up to waste. The reason is that upon start-up you get "break through" TDS, which otherwise would be removed by the resin. I use a tee valve from BRS to divert this first five minutes.