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Re: PH crashing up?

C. Alan wrote:

The water I am using is a mixture of RO water, and tap water. I add a little baking soda, Kent's RO right, and some Kent's PH control Minus. After mixing for about 24 hours, my change out water has a Ph of around 6.5, A GH of 2, and KH of 2.

What is happening is this: I add my mixed water, and the PH drops down to around 7. Within 24 hours it will rise up to around 8.4! I tested the KH, and it is still at 2 or less in some cases. So what is driving the PH up?

What you're seeing is called "pH rebound" or something close. Basically, the buffer in your tap/tank water is strong enough to throw off the effects of the softer water. I have a nice explanation of what is happening chemically stowed away somewhere. I'll try to find it and send it to you if one of our more chemically enlightened list members doesn't feel called to elaborate.

Are you cutting your tap water with RO water to drive hardness and alkalinity down? If that's the case, I don't see why you would add bicarb and the Kent stuff to the change water. Just add enough straight RO water to your tap water to get the hardness and alkalinity down to where you want it. For the water already in the tanks, do a few changes with straight RO to gradually get parameters down. There's no need to mess with all those chems.
Chuck Huffine
Knoxville, Tennessee