Muriatic acid is compatible with ALL pool treatment systems, even bogus ones like Permasalt.
BUT . . . simply adding acid will NOT lower alkalinity. You need to read the articles linked in this FAQ: http://www.poolforum.com/pf2/showthread.php/191
You should also read the Permasalt info here: http://www.poolforum.com/pf2/showthread.php/29112
Good luck!
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