The DIY Calcium idea first came from the fact that I couldn't use my dual chamber reactor from my 230g (well I could but I think it would a bit of overkill. The rest of it came from the fact that my kalk. reactor was successful.
Originally the plan was to just make a whole new appropriately sized calcium reactor, but then while out shopping I saw a phosban reactor for the first time in person. From there it was some bantering with Krazykuch and then we had a rough idea. In short it was trying to find the most useful and cheap materials with which to make a calcium reactor.
There was really no where to find out how to make it, we just tried it out, and we lucky enough that it worked. If it didn't work I was just going to use the phosban reactor to actually run phosban or something.
Thanks Mik for the compliments. I have a whole tank full of frags to photograph now, so maybe I'll put a few more shots up once my MH comes on for the day.