[Darkblade48]

Try Muriatic acid, no scrubbing involved. I cleaned a saltwater sump with it when I converted it to my 90 freshwater. Looked brand new when I was done. 1 gal bottle is like $8.

If you plan to go this route, please take the necessary precautions as concentrated hydrochloric acid is quite corrosive. The fumes are also quite dangerous.