I may be the last one to know this, but the salt you mix can burn corals if not completely dissolved. I did a water change today and a tiny hunk of salt about the size of an eraser head failed to dissolve. My mom poured the water in the tank and before Iwas able to remove the hunk of salt it disappeared into my frogspawn. I tried to remove it but it was too late for my green with purple tipped frogspawn
One head is almost for sure dead now...I really hope it'll come back 

