Yes, with a heater you need Ca. The reason why was on the old board, but I forget right off hand. I think the best support for it is the SI calcs...it's easy to go corrosive without Ca in the water. From the quickie checks I did before, you'll only need about 150 ppm to keep everything happy.

Maybe Ben can remind me of why this is!

(or maybe he can tell me why i'm wrong!)

Michael