Originally Posted by PCBuds
What about calcium ?
For calcium, I actually purchased a large bag of Caribsea Aragonite sand for my saltwater aquarium a
while back and still have lots of it left and so use that. Aragonite is the most soluble form of calcium
carbonate albeit it's not the least expensive kind of calcium supplement. I already have it so why not.
Dolomitic limestone is what I would use had I not already have the Aragonite and it's what I normally
use when I grow outdoors because it's inexpensive.