Sick boy

Hello I had this particular boy for 2 years. 10 gallon aquarium, planted and cycled ahead of time and resides with 3 otos (otos are not showing any symptoms) temperature is 76f, ammonia 0, nitrites 0, nitrates 20 and Ph 7.4. Ro water remineralized with seachem equilibium.

2 weeks a go started with lethargy and a little bloating so I fasted for 3 days. He improved but last week started to pine cone. I have been doing salt baths (half tsp) and 10 drops of methylene blue in 1 gallon of water for 15 mins. The pine coning has subsided but still lethargic and not eating every day.

I have been keeping fish on and off for the last 14 years. Any sugestions? I am in canada, most meds are outlawed