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.
Don't let the high temp scare you, angels can handle higher than that. I've had them as high as 98 due to a broken heater. Just make sure to have only angels in the tank at that temp. Make sure to have plenty of aeration also, as warmer water holds less O2.
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 gallon. You will have to adjust how much you use when doing water changes. You may want to give this a try.
