The biggest/most common reason for foamy water is detergent/residue from swimming suits/bathing suits. We recommend you to avoid washing your swimming clothes in any kind of detergent & let them air dry. Some other cleaners, products can also cause foaming. High pH is another cause. You can try to use a ‘Defoamer’ but this is only a temporary solution If this problem persists you may want to drain the spa halfway or all the way and try again with fresh water.