05-31-2012, 03:33 PM
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Originally Posted by Olympia
Byron, I've come across a confusing situation. Why would tap water with a pH of 7.4 rise to around 9 after aging in a bucket of water within 24 hours? Could a city add buffer that keeps it rising?
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In this situation, it is due to the out-gassing of CO2. Tap water has CO2 dissolved in it, in varying amounts depending where you are and how they treat the water and how far it travels. CO2 lowers pH by creating carbonic acid, just as happens if you diffuse CO2 into a planted tank. By letting the tap water stand 24 hours, the CO2 will dissipate out, and the pH will naturally rise accordingly, to its actual level. You can also shake it vbery briskly in a jar to out-gas the CO2. And you should always do either before testing pH, in order to get a more accurate reading--as you've seen, it changes.
A change from 7.4 to 9 is quite a bit, and I've no idea if this is solely due to the above of some other additive. Contacting your water folks on this may be advisable, it is good to know just what is in the water.