That is how a lot of the myths get started.....
The hobbyist has an issue-try a treatment, medication...etc....then something bad happens and they associate or blame it on the last thing they tried....
this is how the water change killed my fish myth came about and the fish shop sold me sick fish.....
The water changes didn't kill the fish per se'-it usually can be linked to either a neglected tank that the large water change caused a sudden extreme chemistry change or improper acclimation to name the most common causes.
Things like this are the hobbyist fault-due to neglecting the system, poor understanding...etc......But its easier to blame something else....
Same with new fish added to an established tank-One-they should have been Qt and two-when you place new fish in established tank that may have either high nitrate or different pH and the new fish were not properly acclimated to the new chemistry or the nitrate was really high in the established tank that in turn can compromise the immune response in the fish-the new fish are shocked weaken by the chemistry change-they get sick-then the old fish with the compromised immune response get sick and all the fish end up dead or sick....Blame the fish shop....when it was the hobbyist fault......
Or the myth of how pellets swell up in the fish stomach......doesn't work that way.....Pellets will swell up in water...but the gut contents of the fish isn't water....Its gastric acid and enzymes.....this breaks the pellet down, softens them....
Busting myths is a hard job-especially now with the internet-some of these myths have been told so many times that they are viewed as fact....when its still a myth...
We are limited with a lot of science based facts in this hobby, however, some of it is logic, common sense, understanding of a little chemistry and general knowledge of anatomy/physiology of freshwater fish.....