Someting Wong! If your RO water is PH 10 you need a new membrane or your PH meter is way off? RO water from a good unit will be about 10 PPM and PH 7.
RO is nearly pure water, which has neutral pH of 7. But if it’s exposed to air, RO water drops down to an acidic pH range of 5 – 5.5. Why? Pure water is very hungry. it actually grabs CO2 right out of the air! Within about an hour, a glass of pure RO water can drop from a pH of 7 down to a pH of 5.5 or lower and become acidic water.
I always add 50 PPM of Calcium to RO and let it sit overnight then blend my nutrients. PH when done. It will still wander depending on what is living in the reservoir.