That was what they concluded from the smell and suds. They don't know who did it, exactly what was put in the tanks, or why. A kid who didn't know better or was trying to be "helpful"? A bad joke? Disgruntled customer or employee? Sabotage from one of the other two chain LFS that were within a mile at the time? Nobody knows. Nasty thing to do at any rate.
I recently also visited The Reef Store for the first time. Largest stock of equipment, chemicals, and medications I've seen in BR. Not much freshwater fish, as expected, but they did have some nice bettas from Sunpet. They also had a plant tank. Half was occupied with a ginormous mass of clado, the other half with hair algae. They really ought to fix that since one of their advertised services is on-site planted tank setup and maintenance, LOL! I bought some Flourite Dark, my new favorite substrate, no one else in BR had it in stock. And also braved a purchase of Parrot's Feather from the hair algae side of their plant tank. Still working on getting it algae-free and converted to submersed growth.