Need some help understanding what's happening with my pond. I've read some threads on phyto- and zooplankton and have been monitoring my pond more closely this year. The pond is in central Illinois and is ~1 1/4 ac in size and averages ~10' deep. The pond is a former limestone quarry and the total alkalinity is ~180 mg/l (pm). No need to add lime, ever!

The good news is all the large common carp (not sure if little ones remain) have been fished out. With the carp gone, the water clarity improved greatly as I can now easily see ~4' deep rather than ~1.5' from all the carp-generated suspended solids. The bad news is the aquatic weed growth is on steroids. Early in the spring there was a good phytoplankton bloom light green in color. As the water temperatures increased, the light green color began to decrease as the weed growth began to increase. The water became increasingly clear with the exception of when algae attached to the bottom of the pond began rising and introduced some turbidity. Surface algae remains on the perimeter of the pond in most area and does not look like cyano-bacteria. The water is now once again very clear.

My question is how to stimulate zooplankton growth rather than weed growth? My phosphate level in March was ~0.5 mg/l and has decreased to ~0.25 mg/l. I attribute the decrease in the P concentration to the weed growth uptake. I do not want to add more P since it may result in more weeds instead of more zooplankton. Any recommendations? I feel like I'm missing something fundamental here. Thank you!