If your problem is with the filter flow taking them under, try containing the floaters to a corner or any area of the surface using fishing line tied to 2 suction cups. Keep line straight just at the water surface and roots of the frogbits will keep them within that area.I am having a lot of trouble keeping amazog frogbit alive and healthy my problen is that the leaves keep going under the surface of the water and rotting I havr turned down the flow from the filter but still the same any advice ?