Chasin170, I am not sure what you mean by "bound phosphorus". My guess is it isn't bound, but unavailable to plants because pH and/or sunlight penetration is not in a range for some plants to utilize the available Phosphorus.

If you fertilized hoping to get a planktonic algae bloom, you need the proper light penetration, pH, and nutrients. Phosphorus will most often stimulate a rapid growth of Filamentous algae over planktonic algae's.

Often pH is too low in surrounding watershed soils, which effectively controls the water's pH. Ag Lime applied to both the water and surrounding watershed can very often allow more preferred plant life to grow,

Get a soil test done by collecting soils from several areas within the pond's basin AND the watershed. Allow all the soils to dry, then mix them all thoroughly before getting the combined sample tested.