Thank you so much for this info. I've been fishkeeping for many years and recently had my first experience with Hydra infestation. The Hydra bloomed out of control within just a few days and killed off most of my shrimpletts. I came across your article looking for a solution that was safe for my shrimp and rasboras. I found Safeguard containing fenbendazole and used the measured dosage in your article and
VIOLA...The next morning no Hydra and no harm to shrimp or rasboras
It's been a few weeks now and everything is going strong and no sign of hydra.
Thanks so much for sharing your experience and knowledge.