Quote:
Originally Posted by
jdfloyd45 
Muratic acid is dilute hydrochloric acid , either 1/3 or 1/4. Phosphoric is very weak compared to hydrochloric and is much less effective against calcium which is what we're fighting. The muratic acid does need to be handled with caution for sure but nothing else can compare for curing plaster. It will also dissolve the dust associated with plastering if you brush the pond walls and keep the pH below 4.5 for a couple of days. When I've done mine I try to keep the pH at about 5.0 for the whole time .
A full on resperator is probably overkill outside but a mask and gloves are a good idea. I've worked with hydrochloric and muratic my entire adult life and never had a problem but I've always been slightly afraid of the stuff.