Where do the bubbles come from?
Often homeowners think somewhere there is a pump pumping air into the water so the jets have bubbles. Thats not true today. The manufacturer of the jet uses what is called the venturi effect. What that means is the jet is designed so where the pressured water is pushed through the jet it creates a suction and pulls air from some source.
Below is a common setup and help to understand the piping for the air bubbles.
Shown are the 2 separate parts that make for a hot tub circulation.
First water is sucked through a filter (A), into the wetend pump (B), discharged out the pump (C), into a manfold (D), and into the spa.
The second part is when the water is forced through the jet it creates a venturi affect which causes suction... sucks air to the jet assembly.
So there is a amount of air control (1). Below that is a some type of manifold with lines leading to each jet assembly (2). Those lines connect to each assembly (3).
Result is water and air being mixed and you get water and bubble action.
Some THINK there is a "blower" or "bubble maker" in their spa. There is not. Making bubbles is easier than you thought.
Exception: On some model spas their is a THIRD system that DOES make bubbles. On the seat bottoms there are typically a fitting that AIR is blown through a reverse vacuum cleaner motor and these bubbles are released into the water causing an bubbling action.