A bathwater circulating system has a pump operable to draw fluid in at an intake port and expel it under pressure at an output port. Water- and air-supply conduits feed water and air to the intake port at a rate determined by a flow-restricting air-intake valve so that the pump mixes the water and the air, pressurizes the mixture and thereby dissolves the air in the water, and expels the air/water mixture at the output port. A pressure-reducing valve is connected by an output conduit that extends from the output port to the pressure relief valve and conducts the water/air-bubble mixture from the pump to the pressure-reducing valve without separation of the air from the water and such that the mixture is at least partially depressurized at the pressure-reducing valve such that the air forms microbubbles in the water.

This disclosure relates generally to interchangeable jet modules having improved air and water flow. An interchangeable jet module may include at least one jet, a manifold with a mounting surface for mounting a base portion of the at least one jet, and a jet plate with a mounting surface for mounting a top portion of the at least one jet. The module may also include a first array of air and water chambers underlying the manifold mounting surface, a second array of air and water chambers underlying the manifold mounting surface and in fluid communication with the first array of air and water chambers through a valve, and a third array of air and water chambers underlying the manifold mounting surface and in fluid communication with the first array of air and water chambers and the second array of air and water chambers through a second valve.