Re: PH over 15 - what reduced ph?
adding more or less indicator (or diliuting) will not change the accuracy of the reading, only the intensity of the color obtained. Phenol red is the indicator used for pH in pool tests. It has distinct colors at different pH:
yellow 6.8 and below
yellow orange 7.0
light orange 7.2
orange 7.4
red 7.6
red violet (sort of pinkish) 7.8
violet 8.0
purple 8.2 and above.
If you learn these colors your con't even need the color comparator to test pH! The color for a specific pH is always going to be the same no matter who manufactures the test, only the intensity of the color might differ.
Depending on who made your color comparator and indicator solution the colors obatained might be very intense (such as seen in the better kits from LaMotte and Taylor) or very pale pastels that are often seen in the cheap kits with more dilute indicators. Also, the number of drops added will affect how deep or pastel the colors are. Some kits tell you to add only 1 or 2 drops, others have you add 5. You are looking at the color, not how deep or pastel it is! 7.4 will be orange! It might be a deep orange or a very pale orange but it will be orange. Ditto for the other colors and pH.
Hope this explains it!
Retired pool store and commercial pool maintenance guy.
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