From the archives
http://www.pondboss.com/forums/ubbthreads.php?ubb=showflat&Number=96127#Post96127When Not To Fertilize
Some ponds should not be fertilized. Here are some cases where this is true:
Muddy ponds. Mud prevents sunlight from passing through the water. Plankton must have sunlight to grow. If a pond stays muddy most of the time, do not fertilize the pond until the mud problem is corrected.
Ponds infested with trash fish. If undesirable fish dominate the pond, poison the pond, restock, and then begin fertilizing. Request Extension Publication 1954 for details on renovating farm ponds.
Ponds infested with weeds. During warm months, pond weeds use up the fertilizer that the microscopic plants should get. Therefore, the pond stays clear even after repeated fertilizer applications.
Ponds not fished heavily. Fertilizing a large pond is a waste of time and money if you fish it only occasionally. You just produce more fish that arent caught.
Unbalanced fish population. If the bream population is overcrowded, it means there are not enough bass to keep the bream down. It would be foolish to fertilize if this condition exists. Request Extension Publication 1952 and Information Sheet 1479 for information on how to determine balance and to correct problem populations.
Catfish ponds. It is not necessary to fertilize catfish ponds if a feeding program is followed. Where a commercial feeding program is not followed, fertilize in the same manner as for bream-bass ponds.
Excessive water flow. In some spring-fed ponds, the volume of water flowing through the pond is too high to maintain adequate plankton blooms. In this case, fertilizer is constantly being diluted and will have little positive effect.