Welcome back, Darren...
A few mods have been made to the design since that post
Canadian_Man & I (and I should add mostly Canadian_Man's brain power behind this) have been doing a lot of trial & error ...
The main problem with the air bubbles in the lower chamber was the feed arrangement. Basically the reactor was fed off the overflow and since the output was lower than the top of the reactor a slow siphon was taking place.
Out of necessity, I ended up hacksawing off the end as there were leaks. First off, both CO2 injection and reactor intake are on the pump inlet. The reactor effluent is at the top. The top of the chamber is pressured enough to bring back the water several feet higher than the reactor. The pump inlet has enough suction pressure to draw water in by siphon. In my case I have the feed and effluent in my main tank, the effluent goes right into my overflow standpipe via a small piece of airline tubing. In Jon's case the reactor sits lower than his sump so it just goes into the sump. Same effect though.
We found (see the thread "Reactor feed questions") that the reactors were not capable of handling the line pressure in the sump return line. Problems with leaks, bulging edges, impossible to seal flange, etc.
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.
One added benefit of changing the feed arrangement was that since there are now two inlets on the plumbing, one is a "T" facing upwards and another is a "T" instead of a 90-degree elbow at the end, there are now two places in the plumbing that qualify as "higher than the pump" and the pump is now self-priming without undoing any of the unions.
There are still some things that had I to do it all over again, I might still do differently. But that's hindsight. In all honesty finding the right groove has been a three month nightmare (started this in beginning of September). I only just turned on the reactor for the first time for over 24 hours without some kind of "oh, crap" situation, two days ago!! I'll have to tell you about all my mistakes and "do overs" sometime... but now it is fast fading into obscure memory.
