Just to give the pool store a little credit, if you put pucks in the skimmer and kept your pump running at all times (24/7) and ensured you didn't get a power outage, then they should dissolve slowly enough to not be too acidic. Of course, they probably didn't tell you to keep the pump running and that's where they are seriously at fault.
Also, there are "Smart Sticks" from BioGuard that are designed to be put into the skimmer even if the pump isn't always running. Presumably, they do not dissolve unless there is water flow. I can't vouch for them. It would be interesting for someone to have them in a skimmer, have the pump off, then measure the pH in the skimmer after 16 hours of possible pump "off" time.
Anyway, waterbear's advice is correct, you do not normally put in Trichlor pucks into the skimmer, but I wanted to give more info about that. I had a thermometer corrode in my skimmer due to Trichlor pucks (and who knows what my heater looks like), but I didn't keep my pump running all the time (I only did this once) -- this was before I learned about pool water chemistry and started viewing the Pool Forum. We were all newbies once.
Richard