Total alkalinity

Total alkalinity keeps pH from bouncing. Low alkalinity lets pH swing fast. High alkalinity makes pH hard to move and often leads to cloudy water and scale.

Because alkalinity and pH affect each other, fix alkalinity first, then pH. Raise alkalinity with baking soda. Lower it with acid, and use only the amount the label gives. Check your pool maker or a service pro for the target that fits your surface and sanitizer. Test every week, and again after you add acid.