What is it?

Odours are most often caused by a high level of organic contaminants in the water left behind by users.

Typical spa use obviously creates a much higher level of contaminants in the water than occurs with typical swimming pool use and the aeration and higher temperature of the spa help cause the deposition of skin flakes and oil into the water as well as increased sweating. Obviously the sheer quantity of contaminants and bacteria present in each gallon of water causes a strain on the sanitizer to provide adequate protection and contributes to the need to oxidize or drain and refill periodically.