Cleaning a tank

[iMax]

I recently picked this 29 gallon tank up for free and was wondering the best way to clean this dry gunk off the top part of the glass as shown in the picture.

Thanks

 

[aqua_chem]

I've found there's very little you can't get off of a tank with a razor blade and vinegar.

 

[khartig]

White vinegar is the way to go. Use it straight from the bottle, let it soak for a bit and srub off. I have done some with a new scotch brite pad, the real stubborn stuff may need to be scrapped off with a razor blade. Just use some caution so you don't scratch up the tank.