Put your ballast on the pill....
Simply drop a couple of tablets of swimming pool chlorine or bromine in the ballast tank. Sail for a three or four hours or leave overnight. That will kill all life in the ballst water and won't harm the fiberglass, or the lake life when emptied as the converted gas dissipates in the air, just as it does in a spa or swimming pool.I've used this method in my X for 10 years.