I routinely use the N-2 in my current swim spa (about 2000 gallons) one cartridge in the skimmer basket, with a 1″ di-chlor tablet floater which is barely open and expect excellent and balanced water quality if left unattended for at least 1 month. I have also used in a ski house with the hot tub in sleep mode and had excellent water quality …
https://www.amazon.com/Zodiac-W20750-Nature2-Mineral-Sanitizer/dp/B002IT5JS4

