RO likely isn't the problem. Mine lowered my ph from 8.0 to 7.9 when I first installed it.
What was originally in the bucket? Did you use ammonia to clean it, and leave some residue?
When I had my coral tank, I started using the buckets the aquarium salt came in. Altho well rinsed, they still had a 'cake' of white salt adhering to the sides of the white bucket, and it kicked-up the ph to around 8. (yes, I need new glasses) Had to use vinegar to remove the salts. Just fine, now.

Did you do more than one test? What method did you use to test...strips, liquid, or pen? If you use a pen, do you have a calibration solution?
Might want to check an outdoors spiggot (or one not on the RO system) and do a side-by-side test.
Hope ya get it figured out...not sure I'd want to drink water at a 10 ph, let alone trying to adjust it for the ladies every day.
Rusty Trichome Reviewed by Rusty Trichome on . New RO system raising ph Just picked up a 100 gpd ro system. Ran it for about 40 minutes first to clean it out like the instructions said, then filled up a 5 gallon bucket. Ph'd the water after and the filter raised it from the 7.3-7.5 range to 10. Is this normal? Do I just need to let it run awhile to clean it out? Rating: 5