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Re: A guess...

Posted By: Alistair <amckerr@hotmail.com>
Date: Wednesday, 31 March 1999, at 7:08 a.m.

In Response To: Re: A guess... (Wintek)

THe whole subject of water treatments has been bothering me for months. I take your point about commercial pH changers but one thing - regardless of what form of phosphate you add the pH of the water always drifts back to around 7.8 which is the equilibrium point of the phosphate buffer equation. Its initially reasonably easy to establish a fixed pH, but as soon as you add organic activity the carbonate and phosphate buffers start to interact and hey presto - ph 7.8. The commercial pH changers are a con because of that. If you didn't keep fish in the resulting water it would be fine, be we do and so the pH cannot stay constant. Have a look on the Krib for a more detailed explaination (bizzarely enough under the plants section).

As to my water softener its a liquid chemical not an ion exchange product. I think you may be right about the hydrogen phosphate, I will dig some more (or more accurately harass my dad to find out some more - got to keep the retired busy!). Either way, the softner I use does not contain phosphates - I did some tests and an aged sample showed neglible levels (<1ppm).

The thing I missed which you have pointed out is the disparity between the KH and the pH. I think I will try to call someone at the water company. However, the reaction is not just limited to water from my area. The same result happens in a number of different areas (different water co's) and the literature that comes with the softener also says this always happens. It must be establishing a buffer of some type (as soft water has virtually no buffering capacity) but I am jiggered if I can figure out which one. Dang! How about its adding (releasing?) carbonate ions somehow? The equilibrium point of a straight carbonate buffer is about 6.5! With virtually nothing else present to upset the equilibrium, the removal of calcium ions releases carbonic acid somehow which dissociates to carbonates and bingo pH 6.5. With virtually no buffering originally perhaps the pH of 7.8 is a red herring (or loach)?

Who knows? The search contiues. Over to you. Alistair
 

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