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Old 02-11-2012, 08:19 PM   #1
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Default PH Test and Chlorine Test Conflict

So my Precision Labs PH test paper is turning purple which is not an option on the test scale (4.6-6.2). Either my H2o is sitting at a PH of 9 or there is an error. The internet says that high chlorine can turn the paper purple. However, the chlorine test paper indicates the H2o is below 10 p.p.m. which is pretty normal. The local municipal water report says actual chlorine levels are close to 2 p.p.m. so what the deuce is going on?
We just moved here and my last batch of beer tasted off and I'm considering adjusting the gypsum this time but don't know where to start because of the off test results. The other option is just boiling the water out or using mainly bottled water. By the way, I'm just brewing with extract so is it even worth worrying about. Any thoughts?

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Old 02-11-2012, 08:51 PM   #2
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Chlorine is a powerful oxidizing agent - that's why it is in your water. The dyes used to signal pH change in test strips etc change color as they change protonated to unprotonated form (as a function of pH) but as most of them are fairly hairy organic molecules they can be reduced or oxidized by the appropriate reducing or oxidizing agents. Blue litmus paper (wet) ought to turn red when exposed to chlorine as hydrochloric and hypochlorous acids are formed but it turns white instead. I expect you are seeing something like this.

But strips should not be used for measurement of pH in brewing. They simply are not accurate enough.
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