testPlanktonic – The type that changes the water color. Usually green (pea soup) or brown or even red. Filamentous – The type that is mat forming. Prior to forming surface mats it may appear as stringy strands beneath the surface often attached to dock legs,...Generally you should apply when the weeds are actively growing and the water temperature approaches 60° F.Apply consistently across targeted area. Apply with a hand scoop or spreader.With the exception of Sonar, liquid herbicides must be sprayed, covering the entire treatment area evenly. Sonar can be simply poured into a pond in various locations as it stays in the water for up to 90 days.