oh wow i didnt notice you posted your water, ya nitrates in my aquarium are always around the 10s or 20s. It is possible you have a 0 nitrate due to underpopulation and over filtering
It's still showing ammonia 0, nitrite 0 and nitrate 0-3 maybe it's not exactly at 0 but it's pretty close. I'm using the API freshwater master test kit.
yup its fin rot you can tell by the redness in the fin. you should put the aro in a growout tank so it cant get eaten by your other fish. Sadly, Asian arowanas are illegal in the US which is why i didnt bring them into my new house
I think the redness might be from the camera cause I can't see it so either your really good at this or I'm blind. But he's still active and eating so that's a good sign right? But why don't my other fish have it?
Possible immunity in your fish might be the answer. Still add melafix so it can regrow the fins which would take like 7 days- 3 weeks depending on how bad it is