restarting a tank

[usc_lax9]

I have an old 55 gallon aquarium sitting in my basement that i thought would act as a nice frag/quarantine tank for my already up and running 90 gallon tank. It sat half full of fresh water for over a year with no water movement and consequently developed some pretty bad algae (hard) as well as what looks like a water line. I was wondering if there are any methods for making this tank look new. I was considering pressure washing on a light level, but i'm not sure if the glass can take it.

 

[usc_lax9]

 

[Rob.D]

Soak it in vinegar, I think a cup of vinegar per gallon of water is the correct ratio.