It might be ick, an infection of the parasite Ichtyopthirius.7 S+ I# v' y+ a7 V
* s) s8 a+ G. p g- M; }# }! D* lYou 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. 1 s6 B! D/ p' X* j% }: l; D ! x$ p! O# H0 NIt might be hard to keep all the infected fishes, but treatment is necessary to protect uninfected ones. 7 A1 G) K- E# `6 H; \2 v8 L/ i4 I0 |2 P! C
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? $ a, l5 W! e; U4 e$ k9 {' H : e! J0 X3 s: V7 Q7 Q3 U' Y5 M9 L7 wNo, they are cold water fishes, they can survive our winter outdoor as long as water is not frozen and exchange of gases can continue.