Its a difficult one this. I did read that Jeyes was good but as pointed out above it is an irritant and would need to be washed out itself afterwards. I use jeyes for disinfecting my greenhouse and washing it out is a lot easier said than done! Also read that the commercials use stuff that can cause as many problems as it solves and idealy it should be washed off before its put into a lake again! I have a few contacts in the koi carp world and no doubt could find you a product if it puts your mind at ease, however its likely to be expensive as most treatments for koi care cost an arm and a leg! I rarely use keepnets nowadays but a landing net is a must so this is a good thread to get an answer on this tricky subject. Have used net dips at a commercial and to be honest the containers had more crap in them than a sewage farm. Again as pointed out already you need to soak for 20 mins min and no one was doing that as the general concensus seemed to be dip, wet, remove.