Need Help With Making Medicated Fish Food For Parasites

For a while now I've noticed one of my balloon belly mollies being thinner than the others and sometimes swimming oddly, hanging out/swimming at the top of the water, having cloudy eyes and body on and off. Also, the other mollies as well as the one molly often have thin stringy poo. This has gone on for so long, I don't think it could be a bacterial infection.

I tried API General Cure but it didn't seem to cure the stringy poo and made the clouding eyes worse and seemed to be harsh on all the fish. I tried helping out the bacterial problems after with Kanaplex and so far everybody seems to have gotten better yet they still sometimes have that stringy poo so I wanted to make up some medicated fish food since treating them externally didn't seem to help as much.

I've read about making some with Seachem's Focus, Garlic Guard and Metronidazole but I was wondering if I can use the API General Cure instead since I already have it. It says it contains Metronidazole and Praziquantel. I tried researching whether you could or not and only got one place saying not to mix Metronidazole with Praziquantel but if that's true then why do they sell medication with them together? Or are they just not good for making food with?

Also, has anyone used these Seachem products to make food? What are your methods for making it? Are fish flakes better to use than frozen food for guppies and mollies?