Can you use muriatic acid to clean plastic lawn chairs and if so what ratio?

Muriatic (hydrochloric) acid is great, and will clean anything that it won't dissolve. But it's VERY DANGEROUS. Even when diluted, it can burn the skin and eyes, and the vapors will choke you. For general cleaning, try Purple Power. It's a lot safer, but still strong enough to take paint offif ou lave it on too long.

You don't have to go as far as muratic acid probably. I use Clorox and water in my back pack sprayer. Spray on, wait about 10 minutes and then hose off with plain water.

Mildew remover from Walmart works wonders on plastic strap furniture.

If it all plastic just drop into the pool then shock the water..should be clean over night..