Hi Simnandlesley I am in york

the idea with f and m is it strips off the mucus from the koi which inturn take the parasites off and kill them as they do not have a host some times that cause white marks like you described .If it is that it will pass within 2-3days ,. how ever koi do get sun burn does your pond have any shade ,If there is i would say it is very unlikely ,
the treatment of f&m is ideal you would have to repeat treament after about 5-7 days ,unfortunately if the koi in the pic has a secondary bacterial infection the treament of f&m would not sort this problem....

hi where are u situated to ??

hi dont know if u got any replies but if i were to guess from pictures i would say unfortunately it is a bactirial problem ...u require a good anti bacterial treatment eg choromine t or bacterad ...it is almost definately a secondary infection which would require treatment asap....the parasites can be treated after ....wasnt sure but in first pic apearred to have tiny white spots on its head .....if this is the case would suggest white spot but without a scope impossible to tell for sure!! If spots are present after treating for the bacterial infection treat with formilin and malachite.....i hope this is of some help if any other help is needed feel free to ask ...simon