I have a 240 gallon reef tank, about 6 months old. Lately, I’ve noticed white deposits on the rock. It’s very white. My maintenance dude thought it could be calcium, but thought that would only happen if my calcium was high, and it’s only at 380. My alk is around 9. Anyone have any idea what this is? It’s in random spots on the rock, but mostly seems to have an affinity for the joints in the scape, which were done with e-Marco 400.