Any decent Hull Cleaner would work. I prefer Marykate On-Off Hull and Bottom cleaner. All they are is a weak acid solution mixed with a detergent.
If you use Muriatic acid, make sure you dilute it. When you dilute it, make sure you add the acid to the water. You never add water to acid. Also, when you mix acid to water, it will generate heat. Make sure your container can take the heat. Do not leave it on long and rinse with LOTS OF WATER.
You also do not want to get this on your trailer, cement driveway, or anywhere other then the hull. Muriatic acid is very corrosive and be careful of the fumes.
This stuff is not pet or children safe.