Luckily, our PetLand closed. It was only open a couple years, but all their puppies kept dying.
The media was all over that store, and they did a great job of exposing it. People pretty much boycotted the store. I never saw anyone in the parking lot after that. I never actually went to the store, but it was in one of the busiest areas on the west side of our city.
If I were you I would take pictures of the dirty water. Mail them to the manager with a note (see if you can get maybe some local friends/betta lovers to sign a petition stating they are disturbed by the treatment of the fish). I would also mail a copy of the images to the PetLand corporate office, along with any signatures you get.