It is, because everybody already has pH down(phosphoric acid), pH up(potassium hydroxide) and a huge (I believe 25lb) bag of plaster of Paris costs $20, Epsom salts Cost $4 for a 5lb bag at CVS, where you'll almost never run out and it adds the -SO4 anion which promotes the production of...
Why not just make some anhydrous MgSO4 from epsom salt by heating it in the oven on broil for a few hours until it looks like chalk (dissolves much easier) and as for the Calcium portion you can dissolve gypsum CaSO4 in phosphoric acid, making it water soluble. Gypsum is just plaster of Paris...
I'm already doing it with 12 100w COBs. All you'll need to add is a small car radiator. I'm using one from a honda civic. You don't even have to go as far as welding the aluminum. You can just mix epoxy with plaster to make a putty and plug the ends with that, having an exposed flow tube on...