About this deworming med, is it safe to be administered in the main tank? Most importantly, is it safe for the BB in filters?
Where do I get one of these meds and how to use it?
Yes, and yes. As far as where to purchase, you don't live anywhere near me, so I have no idea how to answer that? Locally? Online? Whatever works.
Praziquantel (PraziPro) works well for tapeworms, for roundworms you need to use something like Levamisole. Search some of my previous posts for info on both meds. Without ruling out worms there's not much more I can offer. A 5" male FH at 1+ years of age is not normal. Good luck.