Just installed a new RO system

[ALToronto]

And the pH is 8.5. Unfiltered water pH Is 7.3, and when I was using a jug water filter (ion exchange), filtered water was clocking in at 6.7.

I checked my pH meter with store bought distilled water - 7.0 on the dot. What gives with the RO? The 8.5 reading was after the initial tank flush, and the TDS reading was 12 ppm (down from 136 for cold tap water)

[james mickelso]

Having worked in the water field for 30+ years I would have to say you read the filtrate instead of the product. Easy to do. There isn't anything in the filters to change the ion levels so you had to read the filtrate with all the removed material. Run the backwash again then read the product. How many stages does your system have? Is it a home system or a commercial? How many GPD does it produce? I've thought about getting one for a long time but hesitated due to cost. But now that I only have around 50 orchids instead of over 450 I've been thinkiout it again. I've watered using the dunk method for ages with few ill effects.

[ALToronto]

James, thanks for your response, but we hooked up the system correctly. The filtrate goes into the drain pipe, we don't even see it (but we do hear it). This is a 5-stage undercounter system with its own little tap, and the storage tank (4 gal) is between the 4th and 5th stages.

Besides, wouldn't the filtrate have a higher TDS reading than the tap water we're filtering?

[james mickelso]

Yes. The product should be very low in TDS and the pH should remain relatively unaffected. The backwash is where your pH would increase as this is where the salts and metals are going in a more concentrated amount. The machine from which I get my RO water starts around 7.8 and is around 7.2 when I get it. The TDS starts around 350 ppm (city water) and ends up around 20 ppm. My orchids really took off once I started using the RO instead of city water. Here in SoCal we are at the end of a 500 mile concrete ditch that delivers raw water from NorCal. Most of SoCal gets their water from MWD in LA. Tastes terrible too.

---------- Post added at 12:00 PM ---------- Previous post was at 11:46 AM ----------

pH Lower after RO - DoItYourself.com Community Forums I'm not cornpewtor literate by any means. This is the best I could do. All my water books are out in the garage but this is easily understood. Hope it helps.

[ALToronto]

This is why I'm puzzled. I was expecting a lower pH to go with the lower minerals in the water, but instead, it's higher, while the TDS is about 90% lower, as expected.

There is no peculiar taste to the water, so I'm not questioning the filtration system. Just scratching my head over the pH increase.

[james mickelso]

I don't doubt you hooked it up correctly. But just for your own peace of mind, test the backwash. I know. I know. But I have seen it so many times. Test both streams. Higher pH isn't what should happen. Especially that high. Let me know what you find.

[ALToronto]

Here are the values as of 5 minutes ago:

Tap: pH 7.7, TDS 162
RO: pH 8.3, TDS 17
Backwash: pH 8.5, TDS 260

I thought my pH meter was drifting, but I repeated the readings in random order several times, with the same results. Is this something to contact the city about?

---------- Post added at 01:05 PM ---------- Previous post was at 12:45 PM ----------

And just for giggles, I put some water through my old jug filter (IX resin):

pH 6.9, TDS 110

Tested RO again - pH topped out at 7.8. Now I'm really confused.

[Ray]

Don't forget that RO membranes have preservatives in them, so the first several gallons of "pure" water won't be.

I am thinking that you must be getting some sort of contaminant in the water. Absolutely pure water has a pH of 7, and the equilibrium with carbon dioxide in the air gives the water a H2CO3 concentration that should yield a pH of about 5.7.

[james mickelso]

Thanks Ray. That was going to be my suggestion too. A friend of mine who grows incredible bonsai fruit trees swore he hooked up his unit correctly to find out it was backward so I just wanted to mention it. The product should come out with a pH at or lower than the input stream. Even if the water had high amounts of CO2 it would be even lower pH. Interesting problem here. Ray, are you still selling RO units?

---------- Post added at 01:38 PM ---------- Previous post was at 01:32 PM ----------

Just a thought. Seen more than once. Open your filters and make sure it came with media. Most likely as Ray says you have to run a few gallons through it to wash out all the impurities from the manufacturing prossess.

[fishmommy]

RO membranes have a "break in" period - I forget how many gallons but you should see the water quality improve with a little use.


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