Would this still be the case with a Cerges reactor (RO filter housing) and an in-line heater on the 207 outflow? Not sure how many gph of circulation these items would scrub off, but it seems like the 207 might be borderline on a 20 gallon tank with this setup and I wonder whether a 307 would be a better choice due to the added resistance?
Too many posters to cite individually, but I am doing much of what other posters recommend.
I put a 307 on my 29 gallon, knowing it was too much for my UVS and Griggs reactor (blows too many bubbles out) and this may happen with your Cerges and the 207. So, I put the “Y” in the output with a ball valve on the secondary output. The UVS and the Griggs are on the primary output.
I use the ball valve on the secondary output, rather than the throttle control on the filter, because the throttle control needs to be shut off with every filter cleaning and returning it to the desired flow position is difficult to judge (try to find 50% on their throttle control!). If I were you, I’d start with the one output and see if it provides enough flow, at greater than 50% of the rated output, without forcing too many bubbles through the reactor. If you reduce flow by more than 50%, it will burn out the motor faster. If it works, you’re done. If you get too many bubbles, then you can add the secondary output with the “Y” and valve.
I also substituted 5/8” tubing for the corrugated that comes with the filter, but you will have to use hose clamps because their screw-down clamps won’t fit over the 5/8” tubing.