Best to leave plants out of a koi pond, say you need to treat for parasites like trcihodina and have to use potassium permanganate it will kill the plants so will a lot of other treatments, plus koi will much the plants around the base and make the water cloudy. I'm heavily involved with koi and don't many people with raided ponds who have plants
I didn't know it was a Koi pond. I am only speaking from experience with blanket weed myself in just a standard garden pond. Obviously carp will destroy almost any plant....No worries yes I'm sure walshie is a koi pond raised out ground