Why is my hot tub foamy?

Where the foam comes from

Hot tub jets whip air into warm water, so anything that makes the water slightly soapy turns into foam. A small amount of foam that disappears when the jets stop is common. Thick, lasting or dirty-looking foam means the water needs attention.

Common causes

• Soap, shampoo, body lotion, make-up, hair products and deodorant carried in on skin and hair.
• Laundry detergent left in swimwear.
• Body oils and sweat building up, especially if sanitiser is low.
• Old water - after a few months, dissolved solids build up and the water foams easily.
• Very soft water (low hardness), which foams more readily.
• Some drinks spilled in the tub.

How to get rid of it, step by step

• Test the water. Correct alkalinity to 80-120 ppm, then pH to 7.2-7.8, adding one product at a time with the jets running.
• Bring sanitiser into range: chlorine 3-5 ppm, or bromine in the range shown by the app.
• Shock the water with the lid open and the jets running for 20-30 minutes. This breaks down the oils and organic waste feeding the foam.
• Clean or rinse the filter cartridge - a clogged filter holds on to oils. Soak it in a filter cleaner if it is greasy.
• An anti-foam product knocks foam down in minutes, but it only treats the symptom. Use it sparingly.
• If hardness is below about 100 ppm, raise it to 150-250 ppm with hardness increaser.

When to drain and refill

If the water is more than about three months old, or the foam comes straight back after shocking, it is usually quicker and cheaper to drain, clean and refill. Our hot tub refill plan walks you through it.

Preventing foam

• Shower without soap before getting in, and tie back long hair.
• Rinse swimwear in plain water rather than washing it with detergent each time.
• Shock weekly and after busy sessions.
• Rinse the filter every week or two and replace it about once a year.

When to call a professional

If the foam is brown or smells unpleasant after a refill, there may be biofilm in the pipework. A pipe cleaner flush or a service by a hot tub technician will sort it out.

Frequently asked questions