im not sure if this should be in the disease section or here, but anyway, today i just realised that my male in my 8gal divided tank is either tail biting or has fin rot

. i have never had experience with either of these so i was wondering if anyone could help.
i only noticed today. the water is around 78-80 degrees Fahrenheit i have a low flowrate filter and his attitude dosent seem to have changed. ive been feeding him pellets and occasionally, tubifex worms.
all help is very much appreciated

P.S how would i treat it? i do have AQ salt.