Spa plumbing connectors

[Alexr54]

Can anyone tell me what these connectors are for next to the raised spa? Circled in red.

 

[ajw22]

Air bubble controls. Adjusts how much air bubbles you get in the spa jets.

 

[Alexr54]

Thank you!
I’m still learning my system.
So I suppose the caps will let more air in as I loosen them. Not sure what the purpose of it is since the spa also has a blower...

Thanks for the info!