Try some phosophoric acid in that tank dude. Get it at home depot it comes in a bottle called easy prep n etch, its by the paint . If you get a 1/4 gallon, mix it with 3/4 of a gallon of water and pour it in there.
Faster and way better then vinegar.
WAY less dramatic then muriatic acid.
Dont put Kreem in there please!