Now that I have the reactor running, there is significantly less gas trapping at the top of the Rena, but not totally zero.
I have a few photos of my reactor, but cannot figure out how to attach them to this post. It may not look as nice as some of the others, but it is probably the least expensive of this type fwiw. I believe it works just as well.
125 gal; walmart-K/L covered in PlaySand;
Rena Filstar XP3
6x85watt HO flu. 4.08 Watts/gallon
3x 6500K + 3x 5000k 8hrs/day
HP CO2 ~50 bub/min into Rena canister
My Tap H2O = 0% NO3; 2 Gh; 6.8 pH; 0.3 ppm Fe