At least 15 years ago I did my tank in the 65.It was nasty.I used the POR15 kit.I did the first step the acid.Let it set for a day while turning the tank and shaking it.Then cleaned it out and it sat for 2 days in the sun.Then sealed it and that sat fir 2 days in the hot sun.Still looks like the day I did it.It was cheap easy and worked like a charm.The tank is better than new.Just follow the directions.I think at the time it was around 20 bucks.Rocky