Pondweeds often die back during winter season only to regrow in the spring. As suggested get approved for several grass carp and use tilapia or algacides in the spring. DO NOT stock enough grass carp to denude the pond weed. Numbers needed depend on how much weed coverage you need. For small pond weed start with 4/ac. It is MUCH easier to add them, compared to removing them. You want some pond weed present to create good habitat and compete for nutrients and space against the filamentous algae (FA). Unless you want a dense plankton bloom with fertilization, then go for eliminating all the FA and pond weeds then fertilize. Make sure your alkalinity is above 20-30 ppm for the fertilizer to stimulate a bloom. Very important ""Waters that are low in alkalinity or total hardness (below 20 mg/L or ppm) will need liming in order for fertilizers to be effective."" Also if pondweeds or FA are present they will use fertilizer instead of the algae comprising the bloom.

Study the info here for proper pond fertilization. Your comprehension of the info will determine bloom success.
http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=96127#Post96127

Last edited by Bill Cody; 09/01/14 10:28 AM.
aka Pond Doctor & Dr. Perca Read Pond Boss Magazine -
America's Journal of Pond Management