Ok, didn't mean to sound abrupt, but you tend to have a problems and never answer relevant questions when someone attempts to help. Only way we can glean why and where the problem may be, in order to help you.
I know I'm repeating myself, but stop using the pH up, let your tank settle, and try what Kaysie mentioned to raise the pH. Test it every few days and keep a record of it.
We've never had any very low or very high pH readings with our tanks, so never had a problem.
Many people use this method for their tanks (fish and axolotl) rather than pH up, can't remember what the method is to lower it, but also seen it mentioned/used before.