Why does my water keep foaming when it is being used?
What can I do to change it?
Natures 2 system and chemicla within limits.

The foam is most likely comming from body oils, perfumes, deodorants, lotions, etc, from the bathers (including laundry detergents). What I do is have a rule that if you want to use the tub, rinse off first in the shower, and I NEVER use laundry detergent on my bathing suits. I simply rinse them after each use with HOT water and let drip dry. This has virtually eliminated any foaming in any of my hot tubs, keeps the water clearer, and keeps the filters lasting longer.

You can purchase spa defoamers, but keep in mind this is a temporary fix and you will have to use the defoamer often.