Sick Angelfish with Flat Grey Patches and Coughing

[Caite Grace]

Hi all! I've been following the coop for probably 3 years but I am more of a lurker usually😅 I have a sick fish and was hoping y'all could help!

Today my angelfish did not greet me so I thought something must be up. One of them (the smallest and lowest in the pecking order) has two grey patches on the left side of its head, is clamping its fins, and will also "cough" (like gasping or choking but only in spurts and not at the surface). I noticed one of the other angelfish has a thickened slime coat and also exhibited the coughing behavior. So we have a problem but what could it be?!

After doing some research, watching Dr.Ashley's video for a fourth and fifth time, and leaving a message with my local fish vet (who is closed on weekends) I do have a few guesses. My firsth though was hole in the head (based mostly on the placement of the white/grey patches on the head but there is no hole), second was columnaris (based on the description from Dr.Ashley's video with the flat, thickened white/grey patches), and third would be chilodonella (also based on the description and photo from Dr.Ashley's video with the flat, thickened white/grey patches and difficulty breathing).

I do have access to a microscope! I tried to make slides today with scrapings from the sick fish but they dried before I got to the lab...I have a new plan for this and will attempt again tomorrow! (For personal and scientific curiosity) Water parameters from today are listed below and the best photos I could get of my clearly uncomfortable little buddy :(

Water Parameters:

• pH: 6.8
• Nitrates: 20ppm
• Hardness: 300
• Nitrite: 0 
• Ammonia: 0
• KH/Buffer: 100
• Water Temperature: 78.6 degrees F
• Other info: 55g, last water change 2 weeks ago (usually once a month), 2nd round of ParaCleanse for deworming started yesterday, tank occupants are 4 angelfish and bristlenose plecos, have had the fish since April last year so approx 1 year old (they are starting so do some light sparring)

[Colu]

Have you got a better picture it difficult to tell what's going on