I took a hacksaw to it and will rebuild it. To increase flow, I'm going reduce the number of elbows and increase the hose connection sizes, at least on the outlet to the tank because the Fluval ribbed hose can fit around a 3/4 inch barb.
One thing I noticed while taking the reactor apart is there was a very large area for CO2 to accumulate inside the 1" to 2" PVC adapter. See photo. I'll use silicon to fill in areas like that on the rebuild.
I'm a little concerned about drilling a hole in the chamber and pulling the CO2 tubing though. Doesn't it need to be sealed?
No, it does not need to be sealed if done correctly. What many miss is that the Grigg's design has numerous small design features based on the KISS idea. And those ideas have been time tested and found to work. Most failures are not caused by the design but the lack of trust and the way the work is done. When CO2 is injected near the center of the reactor, the tubing can't be placed correctly with the tools most of us have.
The hole has to be small to compress the tubing correctly. To get that oversized tubing through an undersized hole requires using the method Grigg's had worked out. If you can simply push the tubing through the hole, you've missed the point, not followed directions and it will leak! If you have used a fitting to inject the CO2, you have not followed directions and there is a reasonable chance you will get noise as the CO2 doesn't enter the water where the flow is highest.
So my point is that there is one way to build a Grigg's reactor and it works but there are numerous ways to build a reactor of YOUR design and some work while some fail. Your choice but then it is also your head that the blame has to fall on, rather than the Grigg's design.
Again the KISS principal comes into play. Build it as designed and it works so well that it is almost a "standard" in the hobby or build it your way and it may not work as well.
To make it work, you should have to work to get the tubing pulled in to the center of the water flow! If it is easy, you did it wrong!