How To Know When To Shock

[MJK]

I have an ozonator and bromine hot tub system (tabs etc) and have read the advice to shock weekly (I used chorine). Also read if your system works well and maybe usage is low...shocking might not be needed. I wonder if anyone has info on how you know the level of builtup organics and when to shock accordingly or this just a rule of thumb?? I also understand that this is NOT sanitation which the system does as long as there is enough free bromine. I'm a nubbie so thanks. MJK

[chem geek]

That's a good question and for those on the Dichlor-then-bleach method one usually doesn't have to shock so long as they use enough oxidizer so they keep up with chlorine demand and always measure a residual of chlorine. Basically, shocking (that is, oxidizing bather waste) is continual in that situation. For some, adding some MPS occasionally is done especially after heavier bather loads, but it may not be needed if one has patience.

Now for bromine or for people using Dichlor-only after the first month or two, the answer is much harder to give since bromine is weaker at oxidizing bather wastes as is chlorine in the presence of a lot of CYA. If your bromine demand seems to be rising (i.e. daily loss even when not using the tub) or the water quality starts to look worse, then it's probably in need of shocking by a stronger oxidizer such as MPS or chlorine, though in a bromine spa both will tend to just produce more bromine (but at higher bromine levels, oxidation will go faster and hopefully catch up some).