Maybe you should get in touch with Cornell University, they have an excellent veterinary program, rather than basing your movement on hearsay and conjecture.
You wonder what is killing Wal-Mart fish? Here is my conjecture:
They probably don't quarantine, medicate, buy quality livestock, feed properly, have properly educated staff, or provide specific environment for species.
If it is a central system type rack, then without medicating the whole unit, disease can spread thru quite easily. I see this at our local Petco occasionally. If it's lucky enough to have a UV unit are the bulbs getting changed annually?
About the system, it was created for API to use in pharmaceutical experimentation. MARS bought API, and these tanks are now property of either Walmart or MARS. Marineland is a subsidiary of Spectrum Brands Global Pets Group, who are supposed to provide regular scheduled maintenance. I spoke to 12 different Walmart stores Pet Dept managers, and all 12 were 6 months behind in repairs and filter changes.
These are very substantial tanks if they are kept up on. They were built to maintain precise water parameters in order to develop medications for fish in pharmaceutical studies, but at Walmart the bioloads are unpredictable and fluctuating with deliveries suddenly dumped in each week.
What has always baffled me is I tested all 12 stores tank water with my rescues for 6 months and I swear to you, they were never more than a shade off. This is why I have come to suspect ttx