Why??? IMO: mean people suck! (updated)

[Call Me Wesley]

16. Here's some immediate things you can do:

Make a 20% water change. You can use tap water if it's not chlorinated - rain water might be too acidic, which will add to the problem. Put a handful of baking soda in it (will balance out the pH,) and, if you have, some sea salt. NOT table salt.

If you have an air pump, aerate your pond. There's lack of oxygen already. Stop feeding immediately, if you do. If the pond is in full sun, try to shade it.

It might not be soap, it might be organic matter. Do you have a water test kit? And do you have a filter for the pond? Having Kois without a filtration system is almost impossible unless you have a small lake.

Hope this helps. The water change you can do daily until the problem vanishes, and then I'd say once or twice a week, depending on the water volume: The less, the more often.

Edit to add: If it's mainly rainwater you use, always use baking soda. You can't overdo it; an handful per bucket is okay. It will balance the pH at 7.