If you’re in a very hard water area, it might be a good idea to invest in a pre-filter for your hose before you fill your hot tub. This will remove some of the minerals that cause high TA (total alkalinity) and will make balancing your chemicals much easier. Without a pre-filter, you will need to use TA reducer (hydrochloric acid) or pH reducer (sodium bisulphate), also known as pH minus.
If you’re in a very soft water area, you will need plenty of TA increaser (bicarbonate of soda), also known as TA plus.
Fill the hot tub with fresh water. When the water covers the jets/air inlets, you can turn on the heater. If you have an inflatable tub and you’re filling from the hot tap, start off with some cold so that the water hitting the tub’s surface isn’t too hot, and make sure to protect any area of the tub where the hose might be touching. When the temperature reaches 20-25 degrees C, take a dip test with a good quality test strip to give you a starting point. When the tub has finished filling and after you’ve got your starting point, always balance your chemicals in the following order: