The quick answer
Repeated pH rise is often driven by aeration, high alkalinity, new plaster, saltwater generation or fill-water chemistry.
Aeration raises pH
Spillovers, waterfalls, spa jets and turbulence release carbon dioxide from water, which can push pH upward.
Alkalinity influences the trend
High total alkalinity can make pH rise faster in an aerated pool. The appropriate target depends on the system and surface.
New surfaces behave differently
Fresh plaster can raise pH during curing. Follow the builder or surface manufacturer’s startup plan.
Salt systems and scale
Saltwater generation may add upward pH pressure. Cell scale is a warning that balance needs attention.
Use acid carefully
Follow the product label, wear protection and never mix chemicals. Smaller measured adjustments with retesting are safer than guessing.