To control the water quality in your hot tub, you must conduct regular pH determination. You can add some chemical additives to disinfect the water and prevent algae growth, similar to what they do with traditional swimming pools. The pH of the water should be near the neutral levels and should not be too acidic or too alkaline. You can use acidifiers or alkalinizes for adjustments. Chlorine or bromine derivatives are the most common chemicals for water disinfection or regular shock treatments.