Hi. I have four goldfishes (two black, with big eyes, telescopes or some name like that) and one KOI. Yesterday they started to chew koi and they don't doing enything else, just follow and chew the koi. Koi looks good, there is no any hurts or demage on him, but he is upset and and trying to run away from goldfishes. By the way koi is twice biger than goldfishes and they lives together without problem past year. One more information, i changed water in the aquarium 3 days ago, after that these "attacks" became constantly (and before. those goldfishes were chewing koi but very rerly). Do you have any idea what can cause this extraordinary behaviour of goldfishies. Thanks.
very possible, now the aquarium is full with little white balls (maybe that's eggs, i don't know). There is lot of "balls" on plants, stones... But koi i s still upset, goldies still chews him, and he swimms into and trough the plants (he've never done that). Thank you for yoyr reply MC.