Tuzz - the practice of pond fertilization is used to promote phytoplankton blooms; which provide dual benefits.
1) Phytoplankton are the base of the aquatic food-chain. So, the growth-rate of top-line predator fish is benefited by enhancing the base of the food pyramid.
2) Phytoplankton "blooms" help inhibit sunlight penetration to the bottom of a pond, which makes the pond less hospitable to ROOTED plants AND filamentous algae (which normally initiates its growth on the pond's bottom if sufficient sunlight is available).
Some ponds are able to sustain sufficient phytoplankton blooms with little or no fertilization. Other ponds may greatly benefit from fertilizer treatments - namely, from blends bearing a relatively high middle number in the analysis (phosphorus) - which is the most important nutrient for phytoplankton.
HOWEVER, fertilization timing, treatment-rates and application techniques are critical variables that determine whether the practice ultimately provides benefit or causes a catastrophy.
