Country Boy :

An off the wall idea for thought. Most FA forms on the pond bottom and only floats to the top when it has produced enough gas ( not sure if O2 or CO2)which gets trapped then it floats up on its own . If you take the phosphate out of the bottom half of the pond water by pumping Lanthanum Chloride in solution through a hose to 3 ft. deep you may be able to kill the FA base but not the plankton on top. You also may be able to reduce the amount as you will only be treating 1/2 the pond. If your pond has FA all over the surface this may not do well for you.