Air in pipes from solar heater

[Florida man]

My spa has a "bubbler" type fountain. Water from the spa flows into the pool. When the solar panels come on, air is introduced into the system and there is not enough pressure for the bubbler. Eventually, the air is blown out and the bubbler works. This may take an hour or two. I can force it by holding my hand over one of the pool inlets thereby increasing the pressure to the spa. The pipes are above ground by my pump. This is where I think the air collects. Two of the pipes have manually adjustable valves and go to the spa. The other other goes to the pool.

My question is this: Is there a passive device that I can install that will bleed the air from the pipe?

[Poolo]

A check valve on the return line to the spa should do the trick, especially if it is real close to the spa itself.