[Delphinus]

I still cannot completely eliminate the air bubbles in the bottom but I have learned to live with them. At least they no longer grow into a large level drop.

Hmmmm, OK, I lied. I see this morning that indeed the air bubble in the bottom chamber continues to grow. It's very frustrating. The only thing I can think of is that all the air trapped in the media eventually gets sucked down into the lower chamber and then has nowhere to go. Turning the reactor off, the air bubble doesn't seem to want to trickle back up to the top to be able to exit. It just stays in the lower chamber. Short of drilling a hole in the lower chamber, there's no way to get this air out. I even enlarged my holes separating the chambers when I had this apart to try to make the flow through a little easier.

So what gives? Is this an artifact of the design or am I still doing something wrong? What is the risk of leaving the air in the reactor?

BTW, the CO2 injection is already on the inlet side of the pump (as you have suggested). Thus the CO2 does have nowhere to accumulate but the top of the chamber which then gets sucked into the recirc line. It seems I can't completely eliminate a small air bubble at the top of the reactor either but I imagine that in time that bubble may dissipate. It's the air bubble at the bottom which has me frustrated.