Ideal pond clarity should be between 18 and 24 inches. Having a “darker” pond will limit the vegetation in the middle because of the limited sunlight reaching the bottom. However, clarity of less than 18 inches can cause the phytoplankton (onecelled organisms that make the water greenish) to die off causing lack of oxygen in the water. This lack of oxygen can kill everything living in the pond.
A Secchi disk may be used (or made) to measure the clarity at various depths by drilling a hole through a pie pan painted in alternate black and white quarters and attaching a string. A heavy bolt, washer, and nut through the hole adds weight to make the disk sink. The disk is lowered into the water until the white edges can no longer be seen clearly, and then raised just until the edges are once more clearly defined. The length of wet string is measured to get a depth reading. Two ways to reduce clarity and thereby reduce the sunlight’s reach into the pond are fertilization and pond dyes.
A high-phosphorous fertilizer can reduce clarity, but shouldn’t be used if aquatic vegetation is already established as it will encourage too much growth. Dyes can also reduce clarity, but can also shade out organisms used by fish for food. Dyes can make for an aesthetically pleasing pond with colors including blues, greens, reds, browns, and black.
