I don't know if you've treated him yet, but I wouldn't treat with Maracyn yet. That's premature at this point, and it's not really a good thing to start with antibiotics because they can be stressful on your fish.
Start with clean, warm water. Do you have a heater? How often do you clean the tank? You need to do at least one 50% change each week. Fin rot is a result of poor water maintenance. Keep the tank clean with water changes every other day. I'd do 50% every other day for at least a week. If it isn't better, or it's getting worse at all during that period. THEN move to aquarium salt. Add 1 tsp aquarium salt per gallon. You will need to do 100% water changes each day. Treat for 10 days. If you see no sign of improvement, then it's time to use antibiotics. But, his rot doesn't look anywhere near antibiotics at this point. It'll just stress him unnecessarily.
ETA: Also, treat with StressCoat +, double the dosage. It'll help sooth the tears, and encourage healthy tissue growth.