Sanitizer: chlorine or bromine
Every hot tub needs a sanitizer to kill bacteria, and you pick one: chlorine or bromine. Chlorine (usually granular dichlor in a spa) is cheaper and acts fast. Bromine is more stable in hot water and gentler smelling, which is why many spa owners prefer it. They are not interchangeable day to day, so choose one and stick with it; the bromine vs chlorine comparison covers which suits you.
Keep chlorine around 1 to 3 ppm, or bromine around 3 to 5 ppm, and test before each soak. If you dose chlorine, work out the amount from your spa's real water volume with the chlorine calculator; spa volumes are tiny, so small doses go a long way.
Test two to three times a week
Spa water changes fast because the water-to-bather ratio is so high and the heat speeds everything up. Test sanitizer and pH at least two or three times a week, and before every use if the tub sees regular soaking. Strips are fine for a quick check; a drop kit is more accurate when you need to make a real adjustment.
The reading that bites people is sanitizer dropping to zero between tests. In hot water it gets consumed quickly, so do not assume yesterday's level is still there.
Balance pH and alkalinity
Sanitizer only works well in balanced water. Keep pH at 7.4 to 7.6 and total alkalinity at 80 to 120 ppm, the same targets as a pool. Alkalinity buffers pH, so set it first, then fine-tune pH. Use the pH calculator and the alkalinity calculator for the amounts.
Hot tubs tend to drift in pH as they aerate, especially with the jets running, so expect to nudge it more often than a pool. Out-of-range water is the usual reason a spa irritates skin and eyes or will not hold sanitizer.
Shock after heavy use
Shocking clears out the organic gunk that sanitizer leaves behind: sweat, oils, and the combined chlorine that makes water cloudy and smelly. Shock after heavy use and roughly weekly otherwise. You can use a dose of dichlor for a chlorine spa, or a non-chlorine shock (MPS) that lets you soak again sooner.
If the water is cloudy or smells off despite a sanitizer reading, it usually needs a shock, not more daily sanitizer.
Clean the filter, and refill on a schedule
Rinse the filter cartridge with a hose every week or two, give it a deeper soak-clean monthly, and replace it when it stops coming clean. A clogged spa filter is a common cause of cloudy water and weak flow.
No amount of chemistry keeps spa water good forever, because dissolved solids build up. Drain and refill every three to four months for normal use, sooner if it is used hard. A simple rule: divide your spa's gallons by three times the number of daily bathers to get the days between refills. Start from your real volume with the hot tub volume calculator.
Keep the cover on
The cover is not optional. It holds heat so the tub is ready and cheap to run, and it keeps out leaves, dust, and rain that feed the water with contaminants. A good, well-fitting cover does more for both your running cost and your water quality than almost anything else.
Frequently asked questions
How do I maintain a hot tub?
Keep a sanitizer (chlorine or bromine) in range, test two to three times a week, balance pH and alkalinity, shock after heavy use and weekly, rinse the filter regularly, and drain and refill every three to four months. Keep the cover on between soaks to hold heat and keep debris out. That short routine covers it.
How often should I change hot tub water?
Every three to four months for typical use, sooner if it is used heavily. A common rule is to divide your spa's gallons by three times the average number of daily bathers to get the days between refills. Dissolved solids build up over time and no chemistry removes them, so a fresh fill is the reset.
Chlorine or bromine for a hot tub?
Both work. Chlorine, usually granular dichlor, is cheaper and faster. Bromine is more stable in hot water and milder smelling, which many spa owners prefer. Pick one and stay with it rather than switching back and forth. Bromine's stability in heat is its main advantage in a spa.
Why is my hot tub water cloudy?
Usually low sanitizer, a buildup of combined chlorine and body oils, unbalanced pH, or a dirty filter. Test first, get the sanitizer and pH into range, shock the water, and clean the filter. If it stays cloudy after a refill is overdue, fresh water is the fix.
How often should I test hot tub water?
Two to three times a week at least, and before each use if you soak regularly. Spa water changes quickly because the water is hot and the bather load is high, so sanitizer can drop to zero faster than you expect. Always test before adding chemicals.