One of my black aros have had a major fin rot in the past.
Here's what I did to save him;
1. Isolate him to another tank.
2. Treat the fin and tail rot with Potassium Permanganate ( see below)
3. Salt and high tem (84 degrees)
4. 25% WC every day.
5. After 3-4 days, add Jungle Fungus Clear, I used 2 treatments. NO WC for 4 days in between treatment.
6. A week later, go back to daily WC at 25% rate.
7. After about 2 weeks, the fin and tail started to grow back again, I should see full recovery in 1 month.
Why potassium permanganate ? It kills and stop bacteria infection from the outside. Use it to prevent the condition from getting worse. Once everything is stabilize, then treat the fish from the inside (fungus clear)
Take about a pinch of potassium permanganate and mix it with 1/2 up of water.
Get about 2 gallon of tank water and put it on a separate bucket.
Take the fish out, place him on a wet towel. Have a friend to hold the fish down (don;t use dry towel, as the dry towel will get sticky and pull scales off the fish). I also use some stress coat and smear it over the wet towel.
Hold him steady and start applying the potassium permanganate using q-tip around the edges of the fin and tail. DO NOT GET ANY SOLUTIONS TO THE EYE OR GILLS AREA, THIS STUFF IS POISONOUS.
Let it sits for 30 seconds and place him inside the bucket with 2 gallon of water you took out of the tank earlier.
Let him swim around for 5 minutes and place him back in the hospital tank.
After 2-3 days, the fin and tail edges should be black and you shouldn't see anymore fin or tail rotting. Now treat him from the inside several days later and it should make a full recovery.