Using a Secchi Disc to Test Pond Water Clarity

Using a Secchi Disc to test pond water clarity can provide useful information for keeping your pond healthy. A Secchi Disc is made of metal or plastic with contrasting colors that can be observed as it is lowered into the water with a string.  A seldom used coffee or tea cup will work in a pinch.  When the disc becomes difficult to see the depth is recorded and used to chart the water clarity/turbidity. This value will help with treatment program adjustments.

United Science Secchi Disk

Observations & Possible Problems:

• Less than 8 inches of visibility:
  Danger of a fish die-off due to low oxygen levels and increased carbon dioxide values
• 8-12 inches of visibility
  Excess planktonic algae. Lower oxygen levels may occur after sunset until past sunrise
• 12-18 inches of visibility
  Preferred water clarity condition
• 18- +24 inches of visibility
  Planktonic algae are scarce, possible food chain interruption, aquatic weed growth increases

If you measure less than 12 inches of clarity it may be smart to provide aeration to the pond to reduce the possibility of a fish and aquatic animal die off.  When sunlight can reach deeper into the water column the probability of increase aquatic weed growth happens. This condition can be offset by increasing the soil turbidity or by adding a dye colorant.  Water clarity changes are a good indicator of a process in action.