OK maybe I shouldnt have used the word parasite. More like a virus. But there is nothing you said, that hasn't been said already. Stress, diet, water, all have been linked to the cause, and the cure.
As have other things, such as hexamita/spironucleus, although that too has never been proven. And there is a world of difference between a parasite such as hexamita, and a virus. You weren't the only person that used the term parasite, a previous poster went so far as using the term intestinal parasite. If that was the case once a parasite such as hexamita/spironucleus has become systemic, to the point that it has entered the bloodstream & travelled to organs, and the head region (where the pitting occurs) the chances of it eating anything, or even surviving, would pretty much be zero. I personally don't even like using the term hexamita, as there are several types, some only seen in cold water fish.
Below is an article by Neale Monks where he states that the relationship between the two diseases are well established, which I personally think is a bit of a stretch, at least in the case of warm water tropical species of fish.
http://www.fishchannel.com/fish-health/freshwater-conditions/hexamita.aspx
There may be hexamita
like organisms that can cause HITH, but as far as I know this has never been proven, nor have any viruses as far as I know, which is why I asked about parasites. At this point most of the causes are based on nothing more than speculation.
In your case you feel that it had to do with your personal tap water quality, yet that doesn't mean that using water from a hot water tank is going to be the cause in the next persons tank. I've been using warm water for decades, and performing massive water changes, and never seen a case of HITH in any of the hundreds of fish that I have owned.
You mentioned diet, as it did in the link that you provided, yet one of the most important vitamins linked to HLLE by the U of FL wasn't even mentioned in that link. I also offered the OP a commercial diet that has been proven to NOT induce HLLE, which no one else ever has. Not home made, or commercial. Home made mixes that involve adding vitamins & minerals in a willy nilly fashion may or may not even come close to addressing the dietary part of the equation. I was offering up a simple solution to the dietary part of the equation, that has been proven on a scientific level by a third party accredited institution. (U of FL)
This isn't some kind of a pissing contest, I'm attempting to help the OP by offering up some of what I know to be the most current data that is available on this subject.