There are a number of reasons why spa water foams:
1. You have detergent in the water.
Detergent can be found in your swimming clothing, hair, body, sunscreen, lotions and oil based scent.
2. You have oils in your water.
Oils can come from bathers not showering before they enter the spa or swim spa. It can come from un-approved spa scents being used. If you are using scents make sure they are an approved spa aromatherapy and not oil based.
3.pH and Alkalinity not correct
When your spa water goes out of balance it can start to foam as well as cause damage to your spa or irritating rashes on bathers. Test often using test strips designed for your chemical system.