To be perfectly honest I also don't know how the duplication and calcification works here. I put all the atoms in place in the fastest way I could find, then added as few duplicators as would make all the requires waters wet (which had the unintended side effect of making the molecule basically completely water), then placed a single calcifier in the hole in the output and it basically perfectly separated into waters and salts. 

I definitely think that it's possible to get lower on mechanical area. 5 seems incredibly reasonable, and there's probably an obnoxious amount of bricking that leads to a 4. But I'm not really good at bricking and I also don't have a lot of time for this week so this is what I've got