When you turn on your jets does your hot tub look like someone has poured fair liquid in it?
So, one of the main causes of foam is soap powder residue from when your swimming costumes have been through a wash cycle. As the jets beat against your swimwear it aggravates the soap and causes foam. There can be other contributers such as soft water however soap residue is the most common.
Here's how to fix it...
Run your jets with air controls turned on for 10-15 minutes to allow as much foam to build up.
Add 1-2 caps of Spa No Foam
Watch the foam instantly disappear before your eyes!