Sodium Bisulfate and muriatic acid could have a 5 year shelf life, however pH decreasers are acids, and a larger shelf life concern about pH decreasers is the strength of the container. ... So, although pH-Down chemicals last for years, you should probably use them up.

Does muriatic acid get weaker over time?

Forever! It does not go bad. BUT . . . and this is a HUGE BUTT . . . the bottles do go bad, if exposed to sunlight. And, a brittle old bottle can crack open without warning, spilling acid everywhere.

What can you do with old muriatic acid?

In some areas, you can dispose of unused muriatic acid by diluting the solution in water. Once diluted with water, the acid can be safely poured down your drain. Never pour full-strength muriatic acid down a drain or sewer. Doing this can severely damage pipes.