Flourish and PH

Its supposedly inert, and in the 4 tanks I have it in, I havent experienced any drops in pH.
 
here is what I found after trying to test my PH in the tank after using flourish, it trows the test off from what I see.
I know that my tap water ph is at 7, when I add some flourish it tints(yellowish) the test and shows Ph as 6.
Using API liquid drops.
 
Are you testing the pH right adding flourish, and the turbidity is making the results look yellower?
 
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