There are variety of causes that can explain unwanted foaming in your spa. These include the use of certain algaecides, low calcium hardness, buildup of body oils or contaminants, and improper filtration.
Use HTH spa™ Defoamer to remove and prevent foam, or drain spa and refill with fresh water.
Algaecide Use: Be sure to use HTH spa™ Non-Foaming Algaecide to prevent this from occurring.
Improper filtration: Clean your filter with HTH spa™ Filter Cleaner or oxidize organic buildup with HTH spa™ Non-Chlorine Oxidizer.
Low calcium hardness: Raise hardness levels using HTH® Calcium Up.