I have one 4/5" ranchu in 125L tank mostly sitting on the bottom with occasional manic bursts around tank. No visible signs on the body of any problem.
Token plants of JavaFern,Annubias nana, Eloda Densa. 6mm gravel covering : aesthetic not planted. Aerated with Tetra pump.. Cannister filter 400l/p hour
Water is 0.25ppm ammonia ( ammo locked: should be non toxic ( same before and after 60% water change))
Nitrite =0
Nitrate= circa5ppm
PH =7.4
Temp=circa 68F
API Pimafix added to tank water.
one hour methyline blue bath in separate tank.
Have recently lost a ranchu to,what I now believe was ,cotton fungus a seconadary to recent Nitrite spike.
Where to go from here?