Nice that it's back, it used to be my go-to, but sooo expensive now, and hard to find. For what it's worth I've taken to supplementing my calcium reactor substrate with quahog shells from Revere beach. In a nice afternoon in the summer my wife and I collected several buckets worth, enough for several years worth! I rinsed them well, then smashed them up with a sledge hammer until about the size of quarters to half dollars. I put this in the reactor and it breaks down quite well, same as other media...and free. I've not seen any significant change in algae growth. I'm currently using about 1/3 shells, 1/3 recycled Monti and Acro skeletons from the tank, and 1/3 of the Tunze calcium carbonate product.