Mikezxzx

Had my hot tub for two years I live in New Jersey. Never an issue balancing chemicals. Two weeks ago ph shot up. Low alkaline levels. Tried everything. Finally dumped all water and refilled. Tested all good. Second day tested water the ph is sky high again. All I did was add my bromine. Cannot figure this out. Please help. Tried adding alkaline. Before this tried the ph decreaser. Nothing works.