I have dealt with many cases of Hexamita or Spironucleus in angels. Without a microscope & the ability to stain some slides it is impossible to guess which it is, but the treatment is the same.
These internal protizoans have been implicated in HITH, though with angels the pitting rarely gets a chance to manifest. The fish show symptoms of hiding, lack of appetite, and stringy mucosy feces. If none of these are apparent it is very doubtful that it is HITH.
A 3 day treatment with metronidazole, or dimetronidazole which mat be more available in the UK, is a good start on what should be a 10-14 day treatment. I have been using metro to treat angels with internal protizoans for years, this is sort of thing that pops up on occasion when dealing with a larger volume of fish. This protizoan is a common part of the fish's digestive floura, but if the fish is stressed it can get out of hand. Stress lowers a fish's immune response, this is similar to a human letting themself get run down, which lowers the immune response. You are then more suspect to catching a cold or other ailment.
Anyhow, if you like, here is my usual cut & paste that I have been tacking up here for years on treating angels for internal protizoans. I may be wrong, and it may be HITH caused by internal protizoans, but in many years with easily ten thousand angels going through my setup I have yet to see it manifest those symptoms shown in your pictures.
Put the angel in a quar tank, I usually use a 10 gallon. Increase the temp over a day or so to 90-94F. Treat daily with 40 mg/gallon metronidazole, with 50% water changes daily. If the fish isn't eating, don't feed for the first 3 days. After 3 days, get some frozen brine shrimp. Take a portion about the size of a few match heads, and sprinkle on some metro. You have to eyeball this one, make the shrimp look kind of like a tiny powdered donut. Once it thaws, mix it in & feed. Sometimes they still don't eat for a few days, but once they start to mouth the food & spit it out, the meds seem to get in their system real good. Continue medicating the water & food for 7-10 days.
Metronidazole is sold as flagyl, het-a-mit, and a few other names I can't recall offhand, used to treat hexamita & hole in the head. They usually suggest 20mg/gallon, this often isn't enough. Metro deteriorates in 8 hours, so you could do twice daily water changes. I've done this on the weekends when I have time.
I've also added epsom salt while using metro, this helps with any constipation issues, cleans out the digestive tract. I start with 1 teaspoon per 10 gallons of water, increasing by 1 teaspoon daily for 2 more days to bring it up to 3 teaspoons per 10 gallons. You will have to adjust how much you use when doing water changes. You may want to give this a try.
Now, for HITH carbon has been implicated, as well as poor water conditions & a poor diet. This is more often seen in larger cichlids, oscars in particular. The aquarist does not maintain the aquarium properly, and feeds a poor diet, usually feeders purchased from their lfs. The best way to treat a case of HITH is not metro, but immaculate water conditions, along with a vitamin enriched pellet. A high quality pellet soaked in a liquid human vitamin, such as liquid Centrum, is the best diet to feed.
