I have recently moved into a home with an inground pool and spill over spa. A heat pump is attached to the system to heat the spa and/or pool. I haven't really played with the spa too much yet, but I have fired it up a few times and it took about an hour to raise the spa temp 5 degrees. When the system is in spa mode the heat pump comes on and the valve actuators isolate the spa from the pool plumbing as expected. The owners manual for the heat pump states that it is best to leave the spa air bubbles off when attempting to heat the pool because it can slow the heating process significantly. The problem is, I have no idea where the spa bubbles are coming from or how to stop them. There is an air intake (i think) pipe coming out of the ground near the spa, but I don't see any valves or devices that might be part of the "air injection" process.
Is there some sort of voodoo at work here? How is the air injection typically accomplished on a setup like this and what is the best way to temporarily disable it?