How to clean white lines around the tank?

[pokegirl1332]

Hello everyone this is maybe my 3rd or fourth tank and I just moved so setup my old 30 gallon waterbox in the new place and been up about a month (used water from my 2 year old 100 gallon) the tank had this white buildup all around the tank that makes it hard to see certain spots but it’s nearly impossible to scrub off I tried while it was dry and wet I have scrubbers and glass cleaner any idea exactly the best way to clean it please and thanks pictures below

 

[pokegirl1332]

I’m pretty sure it’s like a very hard salt or calcium build up from when I stoped using the tank originally and didn’t drain it all the way but can’t get it off, it’s on the inside and the tank is up and running well just want nice clear glass

 

[reefer0708]

I found this as my best scrapper.. only works for glass though