I've read the article "Internal Parasites: Prevention and Treatment," but I still have some questions:
1) How do I know which medication to use? The article lists Metronidazole and Levamisole Hydrochloride (as a combination), Praziquantel, and Fenbendazole, but do those all do the same thing, or do they treat different types of IPs? Which one is best for this situation? (Any links to Amazon would be appreciated!)
2) I got some PraziPro awhile back, but never used it because the directions said to add it to the tank water rather than to the food. The "Contents" only lists "oxybispropanol (as an inert solubilizing agent) and <5% praziquantel by weight." Is this the right stuff to use if I use Praziquantel, or do I need another concentration?
3) The Prazi- and Fen- directions both say to give a certain amount of meds per pound of body weight, but I have no idea how much my DP weighs. Is there a way for me to weigh him (I do have a kitchen scale)? Or is it better to dose with a certain number of medicine-soaked black worms? And how often/how long should I do this?
4) Could the minnows have gotten IPs from the black worms that they steal from the puffer, or from the snails that my puffer eats? I'm wondering if I need to make changes to his diet, or to the source of his foods.
5) Would it help to do a large water change, or clean any decor in the tank?
Here are a couple of rough pictures of the clear poop in question (it's attached to a chunk of light-colored stuff, maybe normal minnow poop):

