What time you check your pH? Is it a few hours after the light on? If that so, your high pH is indirectly due to high oxygen level produce by plant in the photosynthesis process. Anyway, are you sure the pH value is 8? I wonder whether the test kit expire or ........[] (no offence). By the way, please do not worry your pH too much as it is link to kH which play more important role in your planted tank. Your kH value is acceptable for normal planted tank.
Just my 2 cents worth.
Aquatic plants and LEGO collector.
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