hard water stain

I was just given a 72g tank with the stand for free, but there was a catch. The water mark stain left from a low water because turtles were kept in the tank... Now, I have tried everything that I could think of to get it off. But was only able to make it fade a little... Does anyone have any suggestions on a solution... I have tried vinegar and soap and warm water, CLR...

here is the best picture I could take.
the water line is about 5 inches from the bottom.

 

Try jewelers paste it is very fine and most likely won't scratch the glass. I'm sure it will require quite a bit of elbow grease. Probably get it at Home Depot or a tool store.

 

maybe goo be gone. whatever you use make sure you follow up with a vingear hot bath and such to make sure all nasty chemcials are out of that tank before filling to use.. im surprised CLR didnt work.. you sure your cleaning the rightside of glass. lol worst case scenario maybe make that side the backside.. so its not as visible.. or make a 6" DSB.. goodluck

 

DAWN AND DRAINO and water MIX ABOUT 10% DRAINO -it will remove hard water stain. Works perfect!!!!