Why is my hot tub foamy? Causes and fixes

Foam on a hot tub is almost always something that came in with the people. Soap, shampoo, lotion, sunscreen, hair product, laundry detergent in swimsuits. A few hundred gallons of hot water whipped by jets turns small amounts into a lot of bubbles.

Jacuzzi's advice while it's foamy: skip the soak for now. Here's how to clear it.

What causes the foam

Body and laundry products top every list. Jacuzzi and Arctic Spas name soap, lotion, sunscreen and laundry detergent from swimsuits; Pool & Spa News names lotions and soaps.

Soft water is the other big one. Caldera says water that's too soft causes foam, and HTH lists low calcium hardness as a cause. If you fill from a water softener or have naturally soft water, this may be your answer.

A few smaller causes:

• Some algaecides foam (HTH and Pool & Spa News both mention this).
• A dirty filter lets oils and gunk build up (Arctic Spas, HTH).
• Filter cleaner not rinsed off. Arctic Spas warns about this one, and soap left behind after cleaning can cause heavy sudsing when you refill.
• Old water. The longer the same water serves soakers, the more builds up in it, and Jacuzzi says foam is one of the signs it's time to change it.

Which cause is it?

When the foam shows up is a good clue.

• Foam right after a refill points to filter cleaner or soap left on the filter or shell, or to soft fill water.
• Foam that builds over a few weeks of use points to lotion, hair product and detergent piling up, and to water that's getting old.
• Foam the day after you added a new product points to that product. Some algaecides foam.
• Foam along with cloudy water points to low sanitizer or a dirty filter. Test before anything else.

How to fix it

Work through these in order.

1. Test and adjust sanitizer and pH. If chlorine or bromine is low, the oils and lotions aren't being broken down. The hot tub calculator gives the dose for your tub. Raising a 400-gallon tub from 1 to 4 ppm takes about 0.29 oz of 56% dichlor.
2. Shock the water. Shock breaks down the organic gunk that makes foam. Add each chemical on its own, straight into the water with the jets running, and never mix spa chemicals together in a cup or bucket.
3. Clean the filter. Rinse it, soak it in filter cleaner if it's due, then rinse it very well before it goes back in.
4. Test calcium hardness. If it's low, raise it with a calcium hardness increaser (HTH and Caldera both recommend this).
5. If foam keeps coming back, drain and refill. Arctic Spas calls this the best long-term fix: flush the lines, deep-clean the filter, refill and rebalance.

What about defoamer? It works, briefly. Jacuzzi and Arctic Spas both describe anti-foam as a short-term fix. It's fine for getting through a party, but the cause is still in the water.

How much calcium a hot tub needs

Spa makers don't agree, so use your own manual's number. Here's the spread:

Source	Calcium hardness
Hot Spring (2026 guide)	50–150 ppm (25–75 for salt spas)
Bullfrog	150–250 ppm
AQUA Magazine	150–250 ppm
Pool & Spa News	200–400 ppm

150 to 250 ppm is the most common answer. Hot Spring is notably lower, so if you own one, follow Hot Spring.

Keep it from coming back

Shower before you get in. The CDC recommends it, and it washes off the lotion and hair product before they reach the water. Rinse swimsuits in plain water instead of running them through the wash every time. Keep the filter on its cleaning schedule, and change the water on a schedule too. The hot tub care guide has the formula for how often.

Keep your readings on the test log. If foam shows up every few weeks, the pattern usually points to the cause.