Muriatic acid is highly corrosive to aluminum and should not be used on this metal as it can eat away the soft aluminum. It will also cause the metal to darken or turn black, which is the opposite of what you are trying to achieve.
Providing the damage is reversible, use Alumabrite
to clean and brighten your pontoons. The performance of this cleaner results from a combination of different acids plus other ingredients which include surfactants and inhibitors. It will quickly do the job for you without damaging the metal. It removes oxide, soot, soil, water stains and will not corrode aluminum.Alumabrite
may be applied hot or cold with high pressure sprayer, garden / pump sprayer or brush. (Use only natural fiber brushes). Mix 1 part Alumabrite
to 12 parts water. Increase strength by up to 1 to 5 for heavy soil conditions. Effectiveness is enhanced if hot water is used. Spray or brush on from bottom to top & down again so that surface is drenched. Within 3 to 5 minutes (before mixture gels & streaks) rinse by drenching with clear water from bottom to top & back to bottom.
Thanks for your question,