I have a 450 gallon Cal Spas hot tub and I had a little trouble with the water at first. These are instructions to my future self to fill and adjust the water after emptying the spa.
Fill with cold hard water. Use cold water and do not use soft water. Fill it where the filter screws in to prevent air in the system. The first time I filled the spa I used hot soft water so that I could use the hot tub quicker. It turns out that soft water is hard on the metal components inside the spa and it’s more difficult to get the levels correct. Hot water is also said to be a bad idea. I ended up adding more and more chemicals to the spa trying to get it’s levels correct and by the time the test strips looked right the water was cloudy; all within about 3-weeks.
Check the pH and Alkalinity level with a test strip. The first thing to get right is the pH and Alkalinity. Mine is usually just right when I first fill the spa but can sometimes be a little high.
Add dissolved pH Minus to lower the pH and Alkalinity levels as needed. If the pH and Alkalinity are a little high, dissolve 1-1/2 tsp (1/2 tbsp) of pH Minus in a cup of water and then add that to the spa. Run the jets for 30 minutes. This reduces both the pH and the Alkalinity.
Check the pH and Alkalinity levels again. If you added pH Minus you’ll want to check the levels again after about 30-minutes to verify that the adjustments to the pH and Alkalinity are correct. One dose is probably enough.
Fill the bromine floater with bromine tablets. Once I have the pH and Alkalinity levels correct I add the bromine tablets to the floater and set the floater in the spa.
Shock the water with Chlorinated Granules to raise the bromine level. Because the bromine tablets are slow acting, I shock the water to activate it. I shock it with 1/2 a tablespoon of Chlorinated Granules. These granules came with my spa and they are very inexpensive. My spa also came with Shock Oxidizer but it requires significantly more granuals (12x more) making it cost a lot over time.