pH of RO water?

racoll · Post by **racoll** » 05 Jun 2004, 10:36

i've just got my new RO running at last and the water is giving me a pH reading of 10.54
does anyone know why this is? the tap water is going in at 7.45
i know RO water is unstable but isn't bleach about 10!!!

pleco_breeder · Post by **pleco_breeder** » 05 Jun 2004, 15:38

Are you sure that you're collecting from the correct line? I've seen several units that were plumbed with the collection/waste lines switched. You may want to test the hardness or TDS of the output to verify that it's plumbed correctly.

Larry Vires

racoll · Post by **racoll** » 06 Jun 2004, 13:11

i've tested the hardness and it's definately the right output line. reading of 0Â° dH. the unit also has a DI as well.

thanks.

pleco_breeder · Post by **pleco_breeder** » 06 Jun 2004, 19:36

I'll admit this one has me stumped. I've never seen that happen before. Sorry I couldn't help.

Larry Vires

racoll · Post by **racoll** » 06 Jun 2004, 22:24

perhaps my brand new digital pH meter isn't calibrated correctly? although i was assured it was, and all it's other readings seem ok.

pturley · Post by **pturley** » 07 Jun 2004, 21:39

What is the pH and alkalinity of your tap water?
I do know Sodium ions are small enough to pass directly through an RO membrane, I believe Hydroxide ions can as well (OH-). The RO unit may be stripping out compounds that act as an acid buffer leaving behind and excessive amount of free hydroxide ions.

This would account for this. How quickly will the pH fall with the addition of a weak acid? (IE: Vinegar)

If you could describe you water source (IE: Deep well, limestone aquifer, or shallow well, sandstone aquifer, whatever) that should help narrow it down.

racoll · Post by **racoll** » 09 Jun 2004, 16:27

that definately sounds plausible to me. the tap water comes in at pH 7.45 ish with a KH of 140 mg/L.

i live in the catchment of a large range of limestone hills called the chilterns which obviously creates very hard water.

the pH does drop fast even with a few drops of blackwater extract added to a glass.

thanks for your help.

racoll · Post by **racoll** » 06 Jul 2004, 19:59

i think i may have worked it out! the RO was brand new and the membrane came in a sealed bag of preservative fluid. i washed it through for the recommended number of gallons, but now that the pH has dropped to 6.5 i feel that it was the residue of this fluid that caused the problem.
i hope this helps anyone that may have the same problem.