By "hydrilla" are you guys referring to actual Hydrilla (the exotic) or are you using it in a generic way for plants with the same growth habit? The underwater photos posted on Clear Spring's site show coontail (Ceratophyllum), but it's labeled as hydrilla. Hydrilla is a nasty exotic, while coontail is a native. Hydrilla has sharp edges on its leaves which can cut your hands... I hate diving in that stuff. Coontail's much nicer, though easier to entangle in.