Many years ago I used to keep just guppies which turned out to have hexamita, i.e. HITH in large cichlids. At the time I came across an article which said that the the parasite causing HITH/hexamitta comes hand in hand with the one causing white spot/ ich. This never made sense to me even then as ich is still considered a disease fish only get from the fish shop, and at the time I had my guppies for months, no real sign of ich on them ever.
But since then, even though I came across hex once more in another livebearer-my platies, I always wonder if hex is secondary to another parasite/disease. Water changes help in any disease and hex carrying fish show up the signs when water quality goes down but it is still a a parasite issue I am afraid. I know for sure hexamita meds do help "control" it. help with recovery but I am not so sure it completely eradicates the issue.
There is a strange thing I have found about hexamita, which is only a wild guess. Although I have hard water, the fish I've kept that had hexamita are also hard water lovers which at the same time shared space with soft water fish I kept(still alive for years), the latter never ever showing signs of hex despite their roommates having it, being treated for it and getting better with the treatment.
So were my hard water fish missing a mineral that the others didn't need as much? Either way, water changes are always best at replenishing vital minerals for fish and plants, and perhaps some will say water changes didn't help their issue, all dependent on one's water content perhaps?