White Gunge?

I have 3 turtles in a big tank, one keeps hiding under a fake coral piece in the tank. Him or her is swimming and eating fine, but I took the fake coral out to give it a clean and under it where the turtle hides was white gunge and quite alot of it. Im thinking could it be eggs or something? or is the turtle to young? it is abut 8months old. please help. Thank you!