Bullet proof calcium deposits

[the_real_brian]

I was looking at my tank the other day. The one I'd just finish drilling and filling when I noticed a white film on the inside of the glass. I thought "no problem" and grabbed a razor blade but it had no effect.

The only thing in the tank was live rock so I drained the tank and removed the rock. I then took some vinegar to what I believe to be some type of calcium deposit but to no avail. You can see where the vinegar lightened it a bit but this stuff is going to take something a lot stronger.

Any suggestions? Something that won't eat the flesh off my bones or leave a toxic residue would be preferred.