It might be ick, an infection of the parasite Ichtyopthirius.8 W' T/ Q4 R! u+ R& C& w: C
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You 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.3 D' B! P5 k- r2 J! |
9 Q4 w9 n$ Z5 t* mIt might be hard to keep all the infected fishes, but treatment is necessary to protect uninfected ones.1 h0 ]" k8 x7 G3 n
m0 y4 B: K+ |7 F" N7 kBy 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?: f: T, f% |1 i' x) m& b6 u
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No, they are cold water fishes, they can survive our winter outdoor as long as water is not frozen and exchange of gases can continue.