RO pH

[BlueSkye]

I might be jumping the gun here, but thought I'd put this question out there. So I just bought a new RO system. I tested the Ph of my tap water and it comes in around 8-8.3 When I test the ph after it has ran through the RO system it comes in around 9. When I add Cal/Mag to the water it comes in around 9.5 I calibrated my pen and even tested with the GH solution and I am getting the same reading, so I know its not my Ph meter. WTF is going on. I have run about 3 gallons through the system so far. I am tripping out on the readings. I decided to run another gallon, add Cal/MAg and let it sit over night. I will test tomorrow. Has anyone experienced this. I thought RO water should test lower than what the incoming water was.

 

[albienieves]

Don't worry about the pH of RO water; it is very difficult to accurately measure the pH of high-purity water, particularly with inexpensive, consumer-grade pH meters. They simply don't work well without some ions in the water.

Furthermore, the low concentration of dissolved solids means the pH can swing wildly when anything is added to it: there's no buffering capacity. Once you add nutrients to the water, the pH probe will work better, and an accurate measurement can be made; the pH can then be adjusted to optimize growth.

High purity water *should* have a pH of 7.0 fresh out of the machine (be it an RO unit or distillation unit), but the presence of atmospheric concentrations of carbon dioxide (which forms carbonic acid in solution) will quickly cause the pH to drop to ~5.6 upon exposure to air. With a fresh, clean RO membrane, there may be insufficient buffering capacity and the pH will drop to this point after a couple of hours or so. As the membrane ages, the pH may not move quite so quickly as there will be a higher level of dissolved salts. (Also note that a nice, fresh membrane in the RO unit will lead to water so pure that you can get an "ice spike" when the water is used to make ice cubes.)

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[BlueSkye]

So your basically saying don't worry about pH until u add nutrients? I grow in soil so I don't know if that makes difference. Also i thought adding the cal/mag might help with an accurate reading of pH. Apparently it doesn't help to much. Thanks for the info!

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[albienieves]

Exactly babe's. Add whatever you wanna add, then check your ph. Go up or down, most likely down cause once you add your nutes, your ph will more than likely drop. When it does, simply ph up to about 6.5. Doesn't have to be accurate, just stay within 6.0 to 7.0. I prefer 6.4-6.8.

I'm also growing in soil. I have an organic super soil aka living soil. And believe it or not, I use tap water.

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