I will do this double-check today. Any particular method you'd recommend? What's most accurate without dropping $200 on a Hanna/BlueLab meter?I've been using RO water from my 5 stage RO/Di unit for years. Never, ever, even after 5 days of storage has my PH ever been below 6.5.
You have an issue somewhere. I would start with whatever method you're testing your PH with. Get some new test strips or borrow a buddy's tester or whatever it takes, but get a second test method involved in this, because there's simply no way on this earth any RO water is below 6. If that's the case, it's not worth even using.
BTW - the thing is, I used a calibrating solution on the meter just last week, so I would be surprised if the meter was off..