I have had my tub for three years, over that time all I have added to the water was one tab of bromine in the floater and tossed in a few ounces of "spa shock" every month or so. Water changed 3 times a year. The tub is used about 2 times a week by one person, maybe two.
When it comes to the swimming pool, I check Ph, and chlorine levels, if not algae will grow. The spa on the other hand smells fine, water is clear, and no foam with only what I do above.
I watched the spa video that came with my bro's tub and LOLed at the number of chemicals it advised using, hahaha.