It would help if you provide some more information about your tank:
Tank size
How many fish and what kinds
How long has the tank been set up?
Water parameters: ammonia, nitrite, nitrate, ph, temperature.
What kind of testing equipment do you use? Liquid test kit, or strips?
What kind of conditioner, to remove chlorine and chloramines from the water.
Feeding info: kind of food, frequency.
I know those are a lot of questions, but we need the answers to know what we may be dealing with.
In the meantime I'm going to attach some pics of fish with columnaris.
The cottony areas that occur with Columnaris can be on or around the mouth, sometimes on the body over the back. Sometimes the mouth is not involved. Sometimes it is just that filmy look that you see on the body of fish in the second picture.
If your fish look like this then I would go get antibiotic medicines first thing tomorrow, as soon as you can. I would isolate and treat the fish as soon as possible. This is very contagious so you want to get them out and in the hospital tank as soon as possible. You will need to watch any other occupants of your tank to look for signs of infection.
Get Maracyn and Maracyn II. These two treat gram negative and gram positive bacterial infection. If this is Columnaris then you need to start right away.
Keep their water a bit on the cool side of comfortable for your Angels, as the bacteria like warm water.
Keep their water parameters absolutely pristine. No ammonia, no nitrites, and nitrates at 20 or so. If you are using strips to test then you must get a liquid test kit. API Master is good. Strips are unreliable and give false readings all the time. You really must know just what your parameters are.
Do water changes as big and as often as needed to keep their water perfect. They need this to help them fight off this infection.
Water changes won't interfere with the medicines as they are unavailable after a few hours in the tank, anyway.
Remove your carbon from the filter. Get Prime conditioner, which will help.
It not only removes chlorine and chloramines, but it also detoxifies ammonia and nitrites. You need this to help in case you do have any traces of ammonia and nitrites. Prime detoxifies for about 24 hours, giving you some breathing room to make the water change.
Here's what I'd do:
Do a big water change after you get the meds before you dose the tank.
24 hours later do another big water change, and then dose the tank again.
Keep doing this for more than the 5 days that the packaging recommends.
I'd go at least 10 days.
You should see signs of improvement within 48 hours, maybe nothing dramatic, but they should act like they feel a bit better: more swimming around, less lethargy.
Feed very lightly. Medicated food would be very good if they would eat it. Kanacyn in their food is excellent. Tetracycline, also. Garlic juice on the medicated food might entice them to eat it.
The packets of meds are prepared for use in 10 gallon hospital tanks, so you will have to halve the contents. This is tricky. I poured out the packet on card stock, scraped the powder with another piece of cardstock creating lines of powder, like cocaine linesl. I've never done that... I've seen it in the movies, lol.
I made lines as even in with and thickness as possible, and then divided in half so the dose would be right for the 5 gallon (I treated a very sick Brochis this way and he recovered fully)
If this is columnaris then time is of the essence.
