It's like when we had goldfish when we were younger and my mum thought that she would do them a favour by buying a really good filter and getting rid of their old under gravel one. Of course she rinsed the media out in tap water every water change and us being kids and goldfish being well goldfish, they were massively overfed.
Then my parents divorced, the tank turned green and one by one our goldfish died of what I suspect was columnaris. Me and my younger brother (around 9 and 7) tried to do a water change but we didn't know how.
More than ten years I have three very happy and healthy goldfish who funnily enough actually have the original filter that my mum purchased. Having to watch my beloved pet fish suffer like that was terrible and it made me very disillusioned with pet and fish store staff. My mum feels awful for what her ignorance caused, and it makes me sick to the stomach to think that there are people out there who through malice or sheer apathy can let an animal in their care suffer.
With the internet accessible in most homes now there really is no excuse for ignorance on the subject of fishkeeping.