Just one thing I'd like to note. There's a possibility that metro is not effective against a heavy hex infested fish maybe because the protozoa has a resistance or because metro is not stable for long enough in the water and the parasite survives, especially if treating fish that don't accept food and can't be treated with medicated food.
I made the same mistake. Treated with metro in the water(fish not eating, those that ate were spitting medicated food out and refused to eat it), got no results. Thought it's not hex then, ended up with a few months battle with fish still dying and me trying to figure out what parasites, worms or even bacterial infection they had.
The problem was eventually sorted with a different hex med called JBL spirohexol which was way easier to administer as it needs a one off dose in the water to stay for a week. Fish showed improvement in only a day and all perked up, all deaths halted.
So metro is something I never bought again. These days I treat with Epsom salt soaked food if I see early signs on fish and it works like a charm but then again I know how it manifests on the types of fish I keep. It's either white feces or fish losing bulk weight slowly but surely. Loss of appetite is very late stages of hex....sometimes too late...A fish can be infested for months, half a year before it finally succumbs to it and stops eating. It doesn't always develop fast in my experience. It's more of a slow killer unlike bacterial infections causing the same symptoms.
Hex can be eliminated in high temperature tolerating species by slowly raising the temp to 37C for at least 24 hours, discus keepers recommend for 4-5 days, that's if you are sure there's no bacterial issue involved otherwise it will kill the fish.
Bacterial issue following hex is not uncommon too as the fish's immune system is destroyed from the stress and prolonged periods of non eating.
But I agree that a bacterial issue can cause similar white feces and lack of appetite. However, it kills the fish faster than hex.
Another med, although untried, that may work against hex and is relatively easy to administer, is flubendazole. I haven't tried it myself so can't comment how effective it is but it will purge a wide range of other possible internal worms all in one treatment, possibly the most broad spectrum and relatively harmless med for de-worming. But may need a double treatment for hex.