I have a crack in my marcite (I think it's marcite, LOL) and when I tap on the crack, it sounds hollow. Speculation on why/how it got hollow behind the marcite?
From the side...you can see the wall is bowed out a little....
I've been letting the water level drop b/c I'm leaking .75-1" a day and I was trying to find it. Just noticed the crack (it's in an X shape) today.