How each one behaves in hot water
Chlorine works fast and is the cheaper of the two, but it does not love a hot tub. Heat and the aeration from the jets burn it off quickly, so levels drop fast between doses, and when it combines with sweat and body oils it forms chloramines, which are what give a spa that sharp chemical smell and sting your eyes. Spa chlorine comes as dichlor granules, which dissolve fast and have a near-neutral pH.
Bromine is more stable at high temperatures and across a wider pH range, so it holds a sanitizer level for longer between uses. When bromine combines with contaminants it forms bromamines, which still sanitize and have a much milder smell. It is usually fed from tablets in a floater and activated with a shock, and it costs more per month than chlorine.
Which to pick
There is no wrong answer for a residential spa. In practice:
- Pick bromine if anyone in the house has sensitive skin, if the chlorine smell bothers you, or if you want the sanitizer to hold steadier between visits. Most spa owners who have tried both stay with bromine.
- Pick chlorine if you want the lowest chemical cost, you use the spa often enough to dose regularly, or you prefer the fast action after a heavy-use session.
- Check your manufacturer. Some spas with mineral or ozone systems specify one sanitizer, and some warranties care.
Switching from one to the other
You cannot switch sanitizers in the same water. Bromine and chlorine interfere with each other and the readings become unreliable. The right time to change is at a drain and refill: drain the spa, clean the shell and filter, refill, and start the new sanitizer in fresh water. If you are moving to bromine, establish a bromide bank at the fresh fill so the floater has something to work with.
TrueBlue maintains both chlorine and bromine hot tubs and keeps whichever one your spa uses in range on every visit. If you want to switch, we handle it as part of a Spa Refresh.