Hot tub foam
Hot tub foam forms when jets turn soap, lotion or detergent into bubbles. You can flatten foam for one soak with a defoamer, yet stopping it requires shocking, cleaning the filter, and finally fresh water.
- Primary source: skin and swimsuits
- Soap
- How long does water last before soap builds up?
- Roughly 4 months
- Calcium at its lowest; water that is softer can foam
- 150 ppm
- Drain and refill for dissolved solids
- 1,500 ppm
Why hot tub foam forms
Foam is a bubble layer that will not pop. Anything soapy keeps bubbles intact as air blowers and jets churn the water.
The Hot Spring owner's manual identifies two places soap comes from. Your body is one source, since a soapy film remains after you shower. Your swimsuit is the other, holding onto soap even after washing. The American Whirlpool manual notes hair carries soap and rapid water movement turns it into foam.
Lay-Z-Spa mentions shampoo, deodorant, detergent residue on swimwear and natural oils from your skin. A little residue adds up each soak, so a tub fine last month may foam today.
Hot tub foam causes and fixes
| Cause | How to tell | Fix |
|---|---|---|
| Soap or detergent on swimsuits | Foam builds once the jets run | Before you soak, rinse suits in plain water; shock the water right now. |
| Lotion, makeup, hair products | Foam and haze after a soak | Shower first; shock after busy soaks |
| High pH or alkalinity | pH over 7.6 or alkalinity over 120 ppm | Lower the pH or the alkalinity |
| Soft water, low calcium | Calcium pad under 150 ppm | Add calcium hardness increaser |
| Filter cleaner left in the pleats | Foam appears right after reinstalling a cleaned filter | Rinse the filter until no cleaner is left |
| Dish soap or detergent used on the filter | Foam every time the tub runs | Replace the cartridge |
| Biofilm in the pipes | Foam plus slime or flakes from the jets | Purge the lines, then drain |
| Old water | Water aged 3 to 4 months, or with over 1,500 ppm dissolved solids. | Drain and refill |
Lay-Z-Spa lists foamy water as a sign of high pH and alkalinity, which this row follows. One problem biofilm causes is foaming, according to Leslie's.
How to clear hot tub foam today
- Check the water quality. Use test strips to measure pH, alkalinity and calcium. Correct any out-of-range values first using the chemical calculator.
- Apply a shock treatment. Soap in water can break down with shock, per American Whirlpool. Find the correct dose with the shock calculator. Chlorine shock requires 0.7 oz (20 g) for a 350 gallon (1,320 litre) tub, following the EPA-registered dichlor label dose of 1 oz per 500 gallons.
- Clean the filter by rinsing it. Use a garden hose to spray between the pleats. If you recently cleaned it, rinse again until all cleaner is gone.
- Keep the cover open while you run the jets. Gas from shock must escape. Do not soak until free chlorine returns under 5 ppm.
- Only add a defoamer if you need the tub right now. Follow the dose shown on the bottle. Hot Spring puts liquid defoamer in the filter area while running the jet pump high for at least 10 minutes.
Treat the water with one chemical at a time while the jets run. Do not combine chemicals in a bucket or cup.
Why defoamers are only cosmetic
Also known as a foam inhibitor, a defoamer flattens bubbles. Both Hot Spring and American Whirlpool state it cannot take soap out of the water. Since the soap remains, foam comes back when the defoamer stops working.
These two brands disagree about shock treatments. American Whirlpool states shock can oxidize soap to help stop foam. Hot Spring states only ozone breaks soap down, not any chemical you add. Try shocking once, but change the water if foam returns within days.
Foaming in a hot tub after shocking
Water, air and surfactants are the three things foam needs; these soapy compounds come from lotion, oils and detergent. Frog states shock helps break them down. Jets keep beating air into water full of loosened oils while shock works. Air from jets and blowers whips such water into froth, says Leslie's.
Let the shock work before you try a defoamer. Run jets with the cover off: Hot Spring keeps it open at least 20 minutes after shocking to vent gas. Although defoamers flatten bubbles for immediate tub use, Frog and Leslie's label them short-term fixes.
More soap than shock can handle stays in the water if thick foam persists after free chlorine hits 3 to 5 ppm. Frog suggests a scum absorber, which is a sponge that soaks up oils, or you can drain and refill.
Soap and filter cleaner in the pleats
A filter might introduce foam to clean water. Jacuzzi's filter guide warns that leftover spa filter cleaner causes foaming, so rinse using warm water until nothing remains.
Products found around the house are worse. Rinsing cannot fully remove soap left by dish soap, laundry detergent or all-purpose cleaners, says Jacuzzi. Swap that filter for a new one since it foams the tub every time it runs.
The same rule applies to inflatable tubs in Lay-Z-Spa's E02 guide: rinse the cartridge under lukewarm water, avoiding any detergent or washing-up liquid.
Foam and soft water
Too little calcium in water can also cause foam. The Intex PureSpa manual notes corroded metal parts and foaming water as outcomes of low calcium hardness.
Water is called soft by Frog when calcium drops below 150 ppm, with a target of 150 to 250 ppm. It raises calcium using a hardness increaser like calcium chloride. Hot Spring warns against filling from a water softener because soft water can corrode the heater.
If draining is the better choice
Each soak adds soap until no product controls the foam anymore. According to Hot Spring, the water then gives your skin an unclean feel that cannot be fixed. About 4 months is how long it expects water to last, depending on soap levels.
According to Jacuzzi's water guide, you should drain and refill when foam gets heavy or dissolved solids exceed 1,500 ppm. Use a line cleaner to flush pipes first, then see how to drain a hot tub.
Preventing foam from returning
- Shower before getting in. Hot Spring asks you to wash off perfume, soap, makeup, and suntan lotion first, then rinse sweat away after exercise.
- Rinse your swimsuit using plain water. Detergent used on a suit brings soap into the tub.
- Only use spa filter cleaner on filters, never household soap, and rinse until water runs clear.
- Shock the water about weekly and after heavy use, as Leslie's recommends.
- Maintain calcium between 150 and 250 ppm and keep pH between 7.4 and 7.6.
- You should change water every 3 to 4 months, or earlier for a busy tub. You can figure out your own date.
Common questions
Will shock remove hot tub foam?
In some cases. Hot Spring says only ozone truly breaks down soap, but American Whirlpool says shock can do it. Drain and refill if foam returns a few days after you shock.
What causes hot tub foam after cleaning the filter?
Some cleaner remains inside the pleats. Take the filter out, rinse it with warm water until suds stop coming off, and put it back.
What amount of defoamer should I add?
Use the amount listed on the bottle for your gallons. Both Hot Spring and American Whirlpool direct you to the label instructions, so the dose changes by brand.
Can low calcium levels create hot tub foam?
Yes. Foaming is listed by Intex as a result of low calcium hardness. Check the level, and if the pad reads lower, boost it to at least 150 ppm.