Maintaining your hot tub the same way you maintain your pool can get you into a lot of hot water! A hot tub is not a miniature pool—it has a smaller volume of water and higher water temperatures, bather loads, evaporation rates, and aeration than pools. Think of it this way—two people in a 1514-L (400-gal) hot tub is the equivalent of 200 people in a 6 x 12-m (20 x 40-ft) pool.
As with pools, the most common sanitizers for hot tubs are chlorine and bromine, which are designed to sanitize hot tub water and oxidize any contaminants that may be in the water. Sanitizer levels in a hot tub are higher than a pool because high water temperatures, combined with the turbulent water, reduce sanitizer levels quicker and create more waste in terms of oils, hair, and skin cells. The ideal range for free chlorine (chlorine that is free to attack new contaminants) in a hot tub is 3 to 5 ppm and 3 to 6 ppm for bromine.
If your hot tub looks like you are throwing a foam party it can be a problem. Foaming on the surface of the water is a result of oils and lotions in the water reacting with chemicals in the turbulent water of a hot tub. Adding an anti-foaming agent to change the surface tension in the water easily controls this problem.
Hand-held vacuums that draw in sand and grit when squeezed can also be used to remove debris that has settled at the bottom of the hot tub.
Water clarity can also be a problem in hot tub water when contaminants too small to be filtered out of the water result in cloudiness. Adding a water clarifier rapidly clears up hot tub water by grouping together smaller, unfilterable particles into larger masses which the filter can trap.
Although rarely a problem in indoor hot tubs, algae may develop in outdoor hot tubs.
Superchlorinating the water, scrubbing the area with a brush, and adding a non-foaming algaecide will clear up this problem.
Additional ways to keep hot tub water clean include operating the filter at least two-to-three hours per day and cleaning the filter regularly with specialty cleaners and degreasers.
Hot tub surfaces should also be cleaned regularly to prevent ‘bathtub ring’ from forming along the waterline.
Although the pH levels remain the same for pools and hot tubs, the TA level for the latter should be maintained in the 80 to 100 ppm range. This will keep the pH stable and prevent the formation of excessive levels of calcium carbonate, which cause scaling and cloudiness in hot tub water.
Calcium hardness levels should be maintained between 140 to 160 ppm, which is lower than pools because of the tendency of hot water to scale.
Even the best maintained hot tubs need to be emptied and refilled on a regular basis. This often depends on bather load (the number of bathers who use the hot tub), but a good guideline is to change the water every three months.