I treated my five gallon betta tank using fenbendazole. I researched dosage and mixed 1 gm fenbendazole with 10 oz conditioned water , shook vigorously and added 15 ml to tank. My tank has hydra all over walls and plants. No sign of change in hydra, so after 24 hours added 15 ml fenbendazole again. Still no change next day. My betta looks good. Did remove charcoal filter. What am I doing wrong?