Excessive foam in a hot tub has many different causes including low hardness levels (below 150), high Total Dissolved Solids (over 1500), personal care products, detergents, spilled beverages, and shell or headrest cleaners.
Prevention is the best option to alleviating foam.
Rinse your swimwear well, shower before using the tub, keep hair up and maintain proper water balance.
To correct an excessive foam issue, make sure the water is balanced.
Then add a defoamer or hot tub shock to the water.
If foam is persistent and it’s been more than 4 months since the hot tub was drained, it’s time to drain and refill.