Eating female crickets isn't bad for them, but it is rather annoying because you always wonder when they go to the bathroom. I also try to take out any poop I see in the cage right away so there's no chance for the eggs to develop, even though I don't know the likelihood of that...usually they dry up and die when the waste does.
As far as the dosage of panacur, I'm not sure how much you could administer without a weight. Out of curiousity...about how long is the frog? And is it underweight, overweight, or just right? I could give you a good estimate of how much to give it in comparison to my frogs. And what I did to give it to them was take a credit card or a card that size and slide it in horizontally to open the mouth and just quick shoot the medicine in there. It's easy and harmless...all but one of my frogs took it very well. The one who didn't has always been hyper...but with a little practice it's easily done. I see you had a picture of the dirty water...any way you could also get a picture of the frog? And as far as something swimming in the poop...if that's what the "vets" saw...the panacur will get rid of it. I would probably give it two doses though, give it one dose and then another after a week just to be safe. I was giving it to my frogs every day I believe...but one of my frogs had actual diarrhea so that's the issue with that.
If the frog does have parasites, just watch for weight loss even if there is some type of appetite. That will happen at first, and then the actual loss of appetite will happen. Those are signs of parasites. I guess keep looking through the poop. I will try and get a picture of what my frogs' fecal matter looks like for a comparison. Good luck!