Please help clarify PH reading - The Planted Tank Forum
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post #1 of 4 (permalink) Old 02-09-2005, 04:41 AM Thread Starter
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Please help clarify PH reading


I just test my tap water PH using Aquarium Pharmaceutical test kit. Using the PH test kit the result came out to be 7.2, but using the High PH test kit it came out 8.0. Which one is the correct one?

My KH is 10 (light yellow) - 11 (yellow). Don't know how useful this will be.

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post #2 of 4 (permalink) Old 02-09-2005, 05:54 AM
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After my water had rested for 48 hours I took it to my LFS and had the PH tested, they told me 8.0. Then I used my AP high PH test kit and it came out 7.8. I haven't considered using the low PH test kit but now I'm curious.
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post #3 of 4 (permalink) Old 02-09-2005, 10:38 AM
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If your KH test is correct, most likely, your pH should be closer to 8. You want to use high pH kit if your KH is 10. I believe the range on the high test kit is 7.4 and over. It is very unlikely to have pH of 7.2 with 10dKH unless you inject CO2.

Rest the water for 24 hours (aerate it if possible) before doing the test. Your tap water may contain high level of CO2 hence has lower pH. But after it's out in the open and reaches its equilibrium, the pH should rise closer to around 7.8.
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post #4 of 4 (permalink) Old 02-09-2005, 06:31 PM Thread Starter
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I did let my water settle for 24 hours before conducting the test. I was leaning on the 8.0 number also, the low PH test color seem a bit darker now which mean it's 7.6 instead of 7.2. Since my PH is 8.0, this means that I need to inject alot of CO2 to bring it down to reasonable level (7.2). I don't have a controller, just wondering if it can be done by just put the CO2 injection on a timer?

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