These are all things that I like a lot.
Ok, this gets a bit complicated. Considering I have a ~50Gallon tank, using an Eheim 2217, could you recommend a good, reliable reactor for this setup?
My 2217 was running a 2.5" x 20" Rex Griggs reactor, with no by-pass. I had a single Eheim quick connect that I used to throttle back the filter just enough to avoid a gas bubble forming (better diffusion). This was installed AFTER the reactor, slightly closed to increase pressure inside the reactor, forcing more CO2 to dissolve.
On that same tank, I ran an Eheim 2213 separately to help with any flow loss I was experiencing from a slightly throttled back 2217 plus a fairly large reactor.
Between that, and adjusting when the CO2 turned on, I could get it almost silent (very slight noise, easily silenced when I shut the stand doors). The only thing I could hear, where the CO2 bubbles pushing through the stainless steel check valve I had just before entering the reactor. There were no bubbles escaping the reactor, achieving a 1.2 drop in pH on a 25 gallon tank with ~5 bubbles per second. I could have pushed more into it without issue.
Here's mine, I know its ABS and it should be PVC, but in Canada our PVC selection is very limited / simply not used in most applications (furnace flue venting, hot tubs etc.) Standard fittings are few and far between. ABS is easy and cheap, just have to ensure it's glued very well to prevent leaks. There shouldn't be much pressure in the reactor anyway.
One thing I would change no matter what, would be a by-pass facing up at the very top of the reactor. This allows me to evacuate the trapped air after filter maintenance without having to turn the reactor upside down.