Looking at the first picture I'm noticing some pitting running back from the head, a classic HITH symptom.
A separate tank if possible, bare bottom, you will be doing large frequent water changes, 50% every other day minimum. Get a high quality cichlid pellet, and some liquid vitamins. These vitamins can be found in the childrens section of most any drug store. Soak the pellets with a bit of vitamin, feed this only.
Carbon has been implicated with HITH, remove this if you are running it. I hardly ever run carbon, only using it for limited circumstances.
Hexamita has been implicated in HITH, but it is very much a chicken or egg deal. Many fish live long & healthy lives with this protizoa, and it is often considered a normal part of the digestive flora in many cichlids. In a fish that is ill it will often overcome the fish's natural immunity, thus being seen in excessive numbers. HITH is an illness, and it is near impossible to tell if the increase in protozoan activity contributed to the HITH condition, or the other way around.
This being the case it is advisable to treat with metronidazole as well, if possible. This is most easily accomplished if the fish is still eating, you can sprinkle a bit on the soaking pellets & mix it in. Be aware that while metro is readily available in the US, a prescription from a vet is required in the UK.