What are these lines on the glass interior

[hrdneglcry]

I have what looks likencalcium deposits on the inside of my aquarium. I removed the overflows and used the back for the front because of a badly scratched up aquarium. Not too long ago these lines appeared. Maybe where the overflow attached has some type if channel scratch. But this won't come off with a razor scraper. Any tips? It wasn't alway there.

 

[SlugSnorter]

surface level scratch, or maybe some kind of deposit, could also be salt on the outside of the glass.

 

[hrdneglcry]

definitely inside. probaby a deep scratch from where the overflows attached. maybe calcium. But cannot scrape it out even with a razor scraper

 

[Rick's Reviews]

A razor blade will only clean a flat surface area, can you scratch/feel with your fingernails to see if it's 'inside' the glass?

 

[hrdneglcry]

it definitely is. its right where the overflow was siliconed to thw tank. i have it in all four spots where the overflow connected