Do I Need To Shock An Unused Spa?

[Alphawolf]

When I leave home for a week or 2 at a time, do I need to shock the spa on returning, though it has gone unused? Why is my bromine level dropping so rapidly on an unused spa? Is it my ozonator? I have a spa frog cartridge opened up to number "6" (highest level) and it won't keep adequate levels of bromine after a few days. I can add sanitizer to a level of 4-6 ppm, and within 4 days (nobody in hot tub) it drops to an unreadable level on test strips.

[chem geek]

Ozone breaks down chlorine to chloride salt, but for bromine though it can break it down into bromide salt, it also reactivates bromide salt back to bromine. So for bromine which one dominates depends on the size of the bromide bank. Did you initially add 30 ppm sodium bromide to your tub? If not, you might try doing that and seeing if the ozonator is able to produce enough bromine in the background.

It's surprising, though, that the spa frog cartridge is not able to keep up unless you haven't been adding an oxidizer after your soaks. It takes a lot of oxidizer to get rid of bather waste. So it's possible you've built up so much excess that it uses up the bromine in the days after you stop using the tub. Every person-hour of soaking in a hot (104ºF) spa would use around 16 ppm bromine in 350 gallons if there were no ozonator. With an ozonator it should be half or less this amount needed.

If your disinfectant level goes to zero, then you could also have biofilms causing greater demand on the disinfectant. If so, you can use Ahh-Some just before your next water change.

[ssalv]

I leave my spa for a week + at times and no issues. I do start with a good Bromide bank and will add about 1/2 oz bleach before I leave. The bleach also turns the bromide bank into bromine. My spa is 450 gal and I add 2 oz bromide with every new water and then another 1 oz after 3 months of water use. FYI, my spa frog cartridges are the 200 G and not the 150 so that helps, set to #3 and I change them out every month. How often do you change bromine cartridges, 150 g is good for about 3 weeks, probably shorter set on #6. I also have small ozone injector. Tub is Marquis Epic

Do you ever shock with Potassium perasulfate, non chlorene shock?

My tub runs for 2 hours every day automatically. Does your have an auto filter cycle that will help keep bromine levels up? Can you adjust the cycle to be a little longer.

[chem geek]

You mean potassium monopersulfate, not potassium persulfate which is a different and irritating chemical and not used to make bromide out of bromine.