Lee Brouillet wrote:

The "mud ponds" the Japanese use are finishing ponds - where the koi go to
"finish" before a show. The "mud" is calcium bentonite clay - a very
specific type of clay. It has very high mineral content and has been proven
over the centuries to improve the color of the koi and the luster of their
skin. This particular clay has many uses, and is even sprinkled over food
here in the States as an aid to digestion. Many paste foods include a half
cup or so of bentonite clay as an ingredient. The fish are placed in the
finishing ponds for 6 months to a year, during which time they aren't seen
at all (due to the density of the mud) until the pond is drained for
harvesting. Then it's like Christmas morning!

The koi don't mind "unclear" water (green algae or mud), their owners do
GBG! We don't like feeding "lips" - all that we can see when the water is
murky. We want to see our prized finny pets, so we want clear water.
Actually, if the water was murky, it would probably save their lives, as it
would be a lot harder for predators to see them. The water can be funky (to
us), but as long as the ammonia, nitrItes, pH and DO are in line, the fish
could care less!

Wow! What a great bit of information. Thanks!

- David