fwiw Jim had some conversations with Doug (Deltec) when he got his reactor. Doug basically confirmed that, to a point, the size of the reactor wasn't that important. The main drawback to a smaller reactor was having to replenish the media more often.
Actually in the case of Ca. reactors size does not matter as stated on the Deltec website, instructions:
Tips on use of a Deltec Calcium Reactor
Always keep the unit topped up to the fill line rather than letting the media fully disolve and then replacing a large amount at one time.
The only real difference between one model and the next one up is the volume of media that it holds so if you run you reactor at half full you may as well have bought the next reactor down.
In other words you can only get x amount of effluent from any given reactor, no matter how big or small. Just a little fyi