Murky water and suspended algae
Cause 1: Too much sun
Cause 2: No plants
With more plants, there would be more shade, and the plants would use some of the nutrients that help algae grow. Alas, the fish and turtles also very much like to eat the plants. Not only does this lead to "no plants in the pond", it also generates a big mess, clogged filtration, and recurring cost for replacing plants.
Grow plants in separate containers and add to pond
Fail 1: The animals' (5 turtles, 4 large koi, and many small fish) appetite is much larger than the growth rate of several tubs of water hyacinth.
Fail 2: Even bigger mess.
Install wires and grow grapes along the wires
Fail 1: This provides some additional shade, but not enough to make a difference. Grapes grow densely too late in the year.
Bonus: This is the final piece in the "heron defense system" for this pond.
Bonus: Yummee grapes.
Floating Pond Pland Islands
Resolution: Covers about 1/3 of pond surface. Turtles can get into some of the floats (that's good, they get to eat greens), but not all. Mess is contained and easily removed. Water is getting clearer slowly.
Bonus: It looks very pretty.
Bonus: It was very fun to build.
Special thanks: http://www.pretotyping.org/
Construction of one island
Planning and Materials