Foam is a symptom of two things to my knowledge-
1) Detergent or soap in your spa water- This can be from shampoo, laundry detergent, or any oily residues deposited in the water.
2) Bad water chemistry.
The difference? Soapy foam can be lifted out of the water and has that rainbow sheen under sunlight. Bad H2O chemistry foam often will dissapate in your hands as you lift it out and is often accompanied with milky water and fizziness.
The foam 'remover' is a silicate fluid that releases the surface tension required to form bubbles-- so really, its effectiveness on anything other than soap is limited. Besides, if it IS a chemistry problem, you should test your water for its deficienies and correct them-- before you resort to adding more 'stuff' to your water.