Having balanced water is less important in a hot tub or spa as they should be emptied and re-filled more often than a swimming pool. Every 4 weeks minimum. Also hot tubs are usually constructed of plastics so there is no need to maintain high calcium concentrations to prevent grout loss. However It is necessary to maintain a concentration of alkalinity to prevent the pH fluctuating wildly.

pH
Bromine is an active sanitiser at higher pH than chlorine. Bromine is effective at pH between 7.2 and 8.2. When bromine is used it is not as important to reduce pH.
All chlorine based sanitisers become less effective at killing bacteria and viruses as the pH rises (i.e. becomes more alkaline).
To keep the chlorine working it is recommended that the pH is kept between 7.0 and 7.6. However if spa water becomes less alkaline it also gets more corrosive and less comfortable to bathe in. Also, if pH drops below 7.2 it will start to attack some liners. Therefore, the pH is recommended to be above 7.2. The normal range that a spa water should be kept at is 7.2 to 7.6.

It is difficult to predict how much acid will be required to reduce the pH to a precise level as it depends on what else the water contains. For instance a soft water will require less acid to adjust the pH than a hard water. We suggest adding 50 grams for every cubic metre (220 gallons) and then re testing after 12 hours and re-dosing if necessary. You will soon become familiar with the amount your particular water requires. To dose, dissolve in warm water in a clean plastic container and distribute evenly around the spa with the filter operating.

Alkalinity Level
In areas where the tap water is soft, or if stabilised chlorine tablets (trichloro isocyanuric acid) are used it will be necessary to add alkalinity to the water. Adding alkalinity builder will slowly increase the pH of the spa water. Too high alkalinity encourages scaling of spa heaters. Water with little alkalinity is corrosive to pumps, heat exchangers, concrete and tile grout. The alkalinity should be kept between 80 ppm and 140 ppm. In hard water areas it will already be over this level so it will need to be reduced with pH minus. Alkalinity levels naturally drop in spa water as CO2 is driven off. Most spa operators will need to boost the alkalinity level every week or two.

Alkalinity builder is added direct to the spa. It will sink to the bottom but will quickly dissolve if brushed. 100 grams alkalinity builder will increase alkalinity by approximately 50 ppm in one cubic metre (220 gallons) of spa water.

Calcium Builder (Calcium Chloride)
If you are in a hard water area (an area where you kettle furs up) it is important that you do not let the calcium hardness level get too high to prevent the spa heater from scaling up. This will be difficult in a hard water area where the incoming water has a natural hardness of about 200 parts per million. In this case Stain and Scale Inhibitor can be used to prevent scaling of the heater. Alternatively the only other way to prevent scaling is to use a water softener to reduce the calcium hardness level.

To prevent scale or stain deposit use Stain and Scale Inhibitor
Initial Dose: 50ml per 1000 litres (220 gallons)
Weekly Dose: 20ml per 1000 litres (220 gallons)

To Remove Scale that has been Deposited use Stain and Scale Inhibitor
As a guide add 2 litres per 1000 litres (220 gallons)
Run the spa/hot tub circulation for 24 hours
Drain the spa/hot tub and rinse out before filling.

The calcium hardness level will only need increasing when it is below 10 ppm as this is when corrosion can occur. However it is very unlikely that a water supply will have less than 10 ppm in it to begin with. To increase the calcium hardness levels add calcium builder.

Calcium Builder is added directly to the spa. It will sink to the bottom but will quickly dissolve if brushed. 100 grams calcium builder will increase the calcium level by approximately 50 ppm in one cubic metre (220 gallons) of spa water.