Hi thanks for you reply.
Tank size: 120 litres
tank age: 3 months
pH: 6.4
ammonia: 0 - 0.5
nitrite: 0
nitrate: 10-25
kH: 0-50
gH: 50-125
tank temp: 27 degrees C
Fish Symptoms (include full description including lesion, color, location, fish behavior):
Was fine when I went to work when I...