RO unit startup

[mordor]

I have bought RO unit and I am little bit confused with water parameters I received. It seem that conductivity is quite low in coparison to tap water. I used formula given by SpectraPure I got 88% rejection rate (should be 98% for new unit I guess). The another thing that does not seem to be right is pH. My tap water is 8.6 and water from RO unit is 7.3. I was hoping to get lower pH, is my line preasure too low?

 

[Charlotte]

One idea... There should be instructions for saturating the membrane before you start. Have you done that already?

 

[Neil]

Charlotte might have a point here. The membrane might have to be broken in a little before it is up to par. Are you ariating the RO water before testing? That will drive the pH up quickly without any buffering.

 

[mordor]

I did more gallons since then and I got completely different results now:
- directly from RO unit: pH 3-4, conductivity 100uS, TDS 60
- after 8 hours: pH 5.5, 60uS, TDS 40
- after 2 days: pH 6, 40uS, TDS <10

It seems that RO water with no buffering capacity (KH) absorbs CO2 from air lake crazy so I may have strange TDS reading if I got water directly from unit. After while CO2 vaporises and pH is going higher while TDS is going lower.

 

[aspen]

mordor, are you measuring r/o with a digital ph meter? read the instructions, most won't work properly on water that is so soft. disregard the ph reading until your reconstitute it.

rick