I don't know if Koi will eat it, probably, as they seem to eat everything else. They will most likely pull the plants out of their pots. The link gives you growing instructions.

Here is a link that might be useful: link to pickerel weed

If you put it in pots that are just barely above the water surface, you should be fine.

I have some growing bareroot in river rock and some are in a large pot with clay soil added. The ones in the pot are bigger and greener, but they all grow well and bloom wonderfully. Neither the koi or goldfish bother them.

Thanks hardin i have them in a 1gallon pail(seperate from the pond) for now so they can get established before i decide to do anything yet.