It might be ick, an infection of the parasite Ichtyopthirius. # u* n) ~1 \# J$ r + C( U/ c. V9 G9 _- ]7 S/ `; tYou can increase the water temp up to ~28C and give them drugs (basically Cu2+ ions), plus large quantity of water change. Google for further details. + Y0 A9 _ j! ^* u) m * u+ l6 C9 c# NIt might be hard to keep all the infected fishes, but treatment is necessary to protect uninfected ones. ' b1 S# ]! _$ Y2 t) F7 ^4 e( |2 F' A1 K
By the way, is it necessary to have >20C for koi and goldfish?
Quoted: By the way, is it necessary to have >20C for koi and goldfish?0 M! i# k5 C" v, J3 t
1 G; E/ O; Y6 h& C" hNo, they are cold water fishes, they can survive our winter outdoor as long as water is not frozen and exchange of gases can continue.