Not sure yet. If I had a bigger tank then I might consider and internal reactor and small pump or power head. No leaks to worry about. With a 20g long space is tight.
Most likely a DIY rig. Not sure what the difference is between Rex-grigg,
cerges, and hybrid reactors. I need to read up. There are a few reactor threads I've been following here with some good info.
Whatever I decide on, I was thinking about putting a vent on top to release extra trapped air. But I want to limit the number of connections and entry points (reduce leak potential). I think if I provide enough slack on the input and exit hoses, I should be able to simply invert the reactor to release any trapped gases upon startup. I should only need to do this after cleaning the canister (or other action that would introduce air into the system).
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