Blanket weed (also referred to as string-algae) is a collective term given to a number of very similar algae that both look and behave identically.

Nothing is more frustrating to a pond keeper than nuisance algae, and from your description, it sounds as though your current algae problem is proving to be just that - a real nuisance.

It is fair to say, that blanketweed is the scourge of the koi pond.

Algae problems in koi ponds have risen to become one of the koi keeper's most common complaints.

Blanketweed is by definition, a weed, that is, a plant that is growing out of place.