For props, get some muriatic acid from any hardware store. Brush or spray on, let it sit, then scrub off with a brush or scrubbing pad. Wear gloves and goggles.
No, I use Klean-Strip Green straight from the bottle. It's already highly diluted. Maybe the stuff from pool supply stores is stronger and needs to be diluted.
Well, there's muriatic acid and there's muriatic acid. It's hydrochloric acid, but diluted by how much? Klean-Strip says it's a trade secret, but somewhere between 10% and 30%. I'd say closer to 10%.
Answers
Dream 'Inn III -- 2008 400 Express
https://rinkerboats.vanillacommunities.com/discussion/11998/prop-cleaning