[Vogata]

Diagnostics is as always impossible to accurate give like this. I guess someone wiser then I will come along.

Take a trip to

http://www.fishdoc.co.uk/index.htm

http://koivet.com/html/articles/articles.php?intro=Articles



It looks bacterial to me; if so you better get it confirmed (lab test), for witch antibiotic / penicillin to use.



- If bacterial skip the biofiltert, trickle to overflow fresh, heated and treated (if necessary) water. This should take all filter problems out off the equation and give opportunity for the best readings in water parameter. Do keep mechanical filtration and steep up flushing.

- Your temperature is for untreated better for bacteria Than Nishikigoi and salt is dependent off strain a double-edged sword. Temperature at 84-85 will often favour Nishikigoi and not the most known bacteria strains

- Some reproduce faster with salt than salt free environment.



PS! Please get more than my thought on both off these statements; I’m not educated in medicine beyond my reading skills and limited experience.