Not having success with BBB in my hot tub

[chem geek]

I'm sorry you aren't having success with BBB in your hot tub. Is your hot tub outside and exposed to sunlight? If so, for how long and do you cover your hot tub when not in use? Can you post a set of typical numbers of spa chemistry parameters (pH, TA, CYA, FC, CC if any, I doubt you have or need much CH)?

Perhaps we can figure out why you were losing so much chlorine. Also, with regard to hot tub itch, this is caused by a particularly difficult-to-kill bacteria (Pseudomonas aeruginosa) so particularly high disinfecting chlorine levels are required and that means not only keeping FC up, but not having CYA too high (if an outdoor spa frequently exposed to sunlight). On the other hand, not using any CYA will lead to a rapid loss of chlorine in sunlight and will also increase its rate of loss through outgassing.

It is true that the chlorine will have a tendency to outgas from the spa more readily due to the higher temperature and the aeration. It turns out that the outgassing is theoretically also very much a function of the amount of chloride ion (salt) that is in the water. If you had a TA of 100 and CH of 30 resulting in a salt level of around 50 (ppm NaCl), then with no CYA this would theoretically outgas chlorine at a rate of around one-twelfth of your FC per day. However, if you had 200 ppm of salt in the water (built up from the chemicals you add over time, including chlorine) then you would outgas chlorine at one-third of your FC per day. If your CH was high, then your salt could be high because CH is increased via Calcium Chloride (and the chloride increases the rate of chlorine outgassing).

It may be that a solution to your situation would be to use a small amount of CYA (10 ppm or less if you can approximately measure that -- most measurement kits only go down to 30 and some down to 20) to cut down the chlorine outgas rate, but not too much since you want high disinfecting chlorine levels. Regularly refreshing the water so that it keeps the salt level down would also help. If you use CYA, then you can safely use quite high levels of chlorine up to 10 ppm and the combination of high FC and a little CYA should give you a decent reserve so you don't "run out" of chlorine. I admit that keeping the "low, but not too low nor too high" CYA level is tricky.

Perhaps others who use BBB to maintain their hot tubs (hopefully successfully) can give you their tips as well. I don't have a hot tub so am speaking from theoretical science, not experience. And I agree with Dave that most people with hot tubs use a Bromine or Bromine/Chlorine combination precisely to combat this "rapid loss of chlorine" problem as well as to reduce the "chlorine smell" (probably from outgassing).

Richard