well for all my diy projects i want to do, first thing i do is look at the unit i would like to get then i look at all the specs, check out other brand and collect pictures, measurments and diagrams. then i draw what i want to make in a part by part drawing, to be able to do this you need to read and fully understand how the object you will be building works. I then make a part by part list, i check the net for the best prices on the parts and then make a total. now that you have plans just order materials and build away!
with this thechnique i now have detailed plans and estimates for:
-protein skimmer
-fbf
-sock filter
-uv stereliser
-bio tower
-complete filtration systems
(all these rated for at least 1000g sw system) sorry man but i dont have plans for calcium reactor but try this and see what you can come up with.