Your hot tub is foamy, cloudy or smells strongly of chemicals, and you are not sure it is safe to get in. Most hot tub water problems come down to three things: too little sanitizer, water that is out of balance, and soap or body oils that build up faster than the filter and chemicals can handle. This page explains what keeps spa water clean, how to tell which cause you have, the numbers to test for, and when a drain and refill is the real fix.
What keeps hot tub water clean and clear?
A hot tub holds a small amount of hot water shared by several people, so sweat, oils and soap pile up fast. Five things keep it clean.
- Sanitizer. Chlorine or bromine kills germs. It gets used up as it works, so the level drops every time people soak.
- Balance. pH, total alkalinity and calcium hardness decide how well the sanitizer works and whether the water scales, corrodes or turns cloudy. Test kits measure these in ppm (parts per million).
- Shock. A larger dose of chlorine, or a non-chlorine oxidizer called MPS, burns off body waste and chloramines. Chloramines are used-up chlorine compounds that smell strong and sting eyes.
- Filtration. The pump pushes water through a cartridge filter that traps fine dirt. A clogged cartridge means less water gets cleaned.
- Fresh water. Soap and other residue build up until chemicals can no longer keep the water feeling clean, so every tub needs draining and refilling on a schedule.
What causes hot tub water problems, and how can you tell?
| Cause | What it does to the water | How to tell |
|---|---|---|
| Low sanitizer | Germs and body waste build up, so the water turns cloudy or smells musty | Free chlorine under 3 ppm or bromine under 4 ppm on a test strip |
| Chloramines | A sharp chlorine smell and eye irritation | The tub smells like chlorine even though free chlorine reads low |
| Soap, lotion and body oils | Foam when the jets run, and a greasy ring at the waterline | White foam builds on the surface each time the jets come on |
| High pH or high calcium | Cloudy water and white scale on the shell and heater | pH above 7.8, or calcium above the range for your tub |
| Low calcium (soft water) | More foaming, and it can harm spa equipment over time | Calcium hardness tests below the range in your manual |
| Dirty or worn filter | Fine particles stay in the water, so it stays hazy | The cartridge is gray or brown, and jets may feel weaker |
| Old water | Water that stays dull and feels unclean on your skin | It stays cloudy even when every reading is in range |
What should I check first when hot tub water looks or smells wrong?
- Test before you add anything. Check free chlorine or bromine, pH and total alkalinity with a fresh strip or kit. We test first, because guessing pushes other readings out of range.
- Sanitizer level. Raise it if free chlorine is under 3 ppm or bromine is under 4 ppm. Those are the CDC minimums for hot tubs.
- Filter cartridge. Pull it out and rinse it. Hot Spring says to clean its cartridges monthly, and inflatable tub makers say weekly or more often. Replace a cartridge that stays discolored after cleaning.
- Alkalinity, then pH. Adjust total alkalinity first, then pH. Taylor Technologies and Hot Spring both give that order, because alkalinity holds pH in place.
- Shock. If the tub smells strong or looks dull, shock it with the jets running and the cover open. Hot Spring says to leave the cover off for at least 20 minutes after a shock so the gas can vent.
- Soap source. Ask everyone to shower before they soak and rinse swimsuits well. Soap comes in from skin and swimwear.
- Water age. If the water stays cloudy with good readings, a clean filter and a shock, it is time to drain and refill.
Safety first. Never mix spa chemicals with each other, and add them one at a time into the filter area with the jets running, as your manual says. Never put pool trichlor tablets in a spa; Hot Spring warns they dissolve too fast in hot water and can damage the tub. Leave the cover open after a shock. Turn off power at the breaker before you drain. CDC says children under 5 should not use hot tubs.
Hot tub water numbers to know
These numbers come from the CDC, the CPSC, test kit maker Taylor Technologies and spa makers’ manuals. Your own tub’s manual may set a slightly different range, so check it too.
| Number | Target | Source |
|---|---|---|
| Free chlorine | At least 3 ppm | CDC |
| Bromine | 4 to 8 ppm | CDC |
| pH | 7.0 to 7.8 | CDC |
| Total alkalinity | 80 to 120 ppm ideal (60 minimum, 180 maximum) | Taylor Technologies |
| Calcium hardness | 150 to 250 ppm for spas (Hot Spring lists 75 to 150 ppm for its own spas) | Taylor Technologies, Hot Spring |
| Maximum water temperature | 104 F | CPSC |
| How often to drain | Spa gallons divided by 3, divided by users per day, gives days between changes (210 gallons and 2 users a day = 35 days) | Intex |
| Drain and refill, hard-shell spa | Every 3 to 4 months | Hot Spring |
Chlorine vs bromine: which sanitizer should you use?
Both kill germs, and the CDC gives a target for each: at least 3 ppm free chlorine, or 4 to 8 ppm bromine. The difference you notice most is smell. Hot Spring’s manual explains that chloramines, the used-up form of chlorine, have a strong odor and are weak sanitizers. Bromamines, the used-up form of bromine, have no sharp odor and still sanitize. Both need a regular shock to clear them out.
Form matters too. Hot Spring recommends sodium dichlor granules for chlorine, because they dissolve fully and are close to pH neutral, and it says not to use bromine sticks or tablets in its spas. CDC’s guidance for public hot tubs says not to use cyanuric acid or stabilized chlorine, because they slow disinfection. Home spa makers still sell dichlor, so follow your own manual and test often. We suggest picking one sanitizer and staying with it until the next fresh fill.
Pool targets are not the same; see our pool chemistry guide.
When should you call a pool or spa pro?
- Cloudy water after a full reset. If the water stays hazy after a drain, refill, new cartridge and correct readings, have the pump, plumbing and filter checked.
- Weak jets or flow errors. Poor flow means the water is not being filtered. Start with our hot tub jets, pump and GFCI guide.
- Stains or scale you cannot clear. Metals in your fill water can stain the shell. A pro can test the source water and suggest a metal or scale treatment.
- Rash or illness after a soak. Stop using the tub. CDC has guidance on hot tub rash and Legionella, which are both linked to poorly kept water.
Pool and spa pros bill by the visit or by the hour, so test and clean the filter first.
Common questions
Will shock get rid of foam in a hot tub?
Shock helps with body oils and waste, but it does not remove soap: Hot Spring’s manual says no chemical you add oxidizes soap, only ozone does. Shock clears body waste, but Hot Spring’s manual says no chemical you add removes soap; only ozone, or its salt system, can oxidize soap residue. A foam inhibitor hides foam without removing the soap. If the water is loaded with soap, its manual says a water change is the fix.
What can I put in my hot tub to get rid of foam?
A spa defoamer or foam inhibitor knocks foam down quickly, and spa makers sell them for this. It treats the symptom, not the cause. Shock the water, clean the filter, and cut the soap and lotion going in, or the foam will come back.
Why is my hot tub foaming so bad?
The usual cause is soap from skin, hair products and swimsuits that the jets whip into bubbles. Hot Spring says low calcium hardness (soft water) can make foaming worse. Old water that has collected weeks of residue foams more too.
Is it safe to go in a foamy hot tub?
Foam by itself is mostly soap and oils, so the real test is the sanitizer and pH. CDC says to check that free chlorine is at least 3 ppm, or bromine is 4 to 8 ppm, and pH is 7.0 to 7.8 before you get in. If those are off, or the water is also cloudy or smells, stay out until you fix it.
How do I fix cloudy water in my hot tub?
Test and raise the sanitizer, then bring alkalinity and pH into range. Clean or replace the filter, shock the water and run the jets. Intex says to change the water when it stays cloudy even with proper chemistry, and Hot Spring lists a drain and refill as the last step.
Is it safe to sit in a cloudy hot tub?
We would stay out. Cloudy water often means low sanitizer, poor balance or a dirty filter, and you cannot see the seat or the drain covers clearly. Test it, fix the cause, and get in once the water is clear and the readings are in range.
Is baking soda a defoamer?
No. Baking soda is sodium bicarbonate, which spa makers sell as an alkalinity increaser. It does not break up foam, and adding it when alkalinity is already in range will push alkalinity and pH too high.