What are the large control knobs on the lip of the spa?
These large knobs are called diverter valves (Ultra Massage Selector). Depending on what spa you have it will either have one or two of these, measuring about 4 3/4″ in diameter. These knobs control water flow to specific spa seat zones. By having the knob in the center position, water flow is balanced between two zones. Turning the knob in either direction causes the water flow to be diverted to that seat section. This allows you to choose a powerful or more gentle massage.