If its for the chaeto dont they consume co2 and not o2? If it's to benefit the tank I think a small pump would be better. Itll provide water movement without the salt creep from the bubbles.
I put two in my 20 gallon fuge. It is covered with a glass plate. No real salt creep. It does not cause the chaeto to tumble. I do it to drive CO2 out of the tank water as the feed air is from outside the home.
Note: my CO2 reactor drips into the same fuge.
I tried putting a power head in the fuge. It gets clogged up quickly with small pieces of macro algae. I grow a combination of chaeto and Ulva in my fuge. I put foam and screens around the pump and it only delays the inevitable clogging. Airstones don’t clog and don’t kill the massive pod cultures living in there.
Here are some pics of air stones in my refugium. Note, all the water coming from the tanks pass through this fuge on the way to the sump. So there are a lot of bubbles just from the water rushing in from the pipes.