A calcium reactor is nothing more than a chamber in which you melt calcium carbonate substrate and introduce the solution back into your water.
Things to consider,
A) It wont leak
B) it has sufficient volume that you aren’t opening it every few months to add substrate
C) the recirculating pump is protected from grit damaging the impeller, pump on top is one strategy that is time tested
D) disassembly for maintenance and adding substrate isn’t overly complicated.
Next component is the Co2 regulator. IMO, for our needs, the carbon doser is the best option for a Calcium reactor, It’s not overly expensive, very consistent and stupid simple to setup.
Lastly is the effluent control. Masterflex paristolic pumps are the top of the line but they are rather expensive, can be loud and are very large. I use manifold pressure from my return pump and a precision needle valve. My approach is smal, silent and inexpensive but does need to be inspected weekly to ensure it hasn’t clogged.
