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Hello, I am looking for help concerning my reverse osmosis system and water pH. I moved from a city with really hard, alkaline water. I use a simple three-stage RO system that worked quite well getting the TDS down below 10 ppm and the pH slightly acid, about 6.5.

The city I live in now has similar tap water. However, my purified water is just as alkaline as tap, above 7.5. The system appears to be working as it reduces TDS from 300+ ppm to under 10 ppm. I've never observed this before and was hoping someone could provide an explanation as to why the pH is not being affected.

How concerned should I be with this higher pH water? I grow many different species of highland Nepenthes and Heliamphora, which I know are very particular to water quality. I have been using the water for a couple of months before I discovered this problem, and the plants are doing fine. I am hesitant to continue using this water, but I am worried about any abrupt changes as well. What should I do?

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I don't have vast knowledge about water chemistry, but to me that does seem a bit odd. I'm guessing that the few remaining minerals in the output water (10ppm) must include those that affect pH slightly.

If the input pH of your new supply is much higher (alkaline), I guess the end result is going to be also higher if affected by this small amount of dissolved minerals?

Do you have the chemistry reports for you water supply (both previous and current property to compare).. these should be easily accessible to the public.

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pH of pour-through water is probably more telling than the pH of RO.  In other words, pH of the root zone is influenced more heavily by the types of media than the water since the RO water doesn't have many ions.

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  • 3 months later...

RO water has no bufferring capacity, so the pH is influenced by any minute substance it comes into contact with.  Even temperature can change the pH of pure water.  Basically i wouldnt worry about it, all you need to know is the tds is low.  As naoki says, it will be acid as soon as it touches the peat in all probability.

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