Re: cleaning my pontoon
The muratic acid solution is the best way to go, but I'd be afraid to give you a recipe i.e. 10% solution, etc. It's pretty dangerous stuff.
I would go to a marine store and get some of their acid based aluminum cleaner and use it. Or, the NAPA aluminum brightener is also very popular stuff. It's all spray on with a yard sprayer, let it sit 5 minutes and shower it with fresh water--no scrubbing. Then repeat if needed.
But I'd start out at the quarter car wash blowing off every bit of crud you can. I'd probably use a bleach solution first to see if it helps.
When you're over, check the toons to see if they're sealed and water free. Leaving any boat in the water scares me a little. I just wouldn't want to buy a used boat to find it has water in the toons.