I keep Prazipro, Jungle Ich Guard 2, and tetracycline. I have never had any fish need anything other than one of those. Prazipro is the best medicine out there for internal parasites, worms, gill flukes, etc. harmless to the fish, and bio bacteria too. I have cured cories, loaches, and scissortail rasboras with it. All living healthy now.
Loaches especially should be treated immediately when you buy them, even if they look healthy at the time, because a lot of them die from skinny disease because no one knows what it is. They just think the loach has something else wrong with it. Then they make it worse by dosing other meds that have nothing to do with why the loaches are dying. I feel really bad for loaches I see in the pet stores who clearly have this parasite, and all they would have to do is treat them, but they don't. Really irks me.
My Toys; 100 gal. Clown Loach tank, 40 breeder community tank, 7.5 gal Emerald Rasboras, & Dwarf Cories, 17 Gal. Aquascaped Rimless Cube, Pygmy Cories, Embers, Dwarf Cories, Amano Shrimp, 3 plant/shrimp tanks, 300 gallon formal water lily pond, 150 gal. pond.