Assuming you copied the directions correctly, it sounds like this medication is meant to be added to the tank water.
If that's the case, I would not use it on the food. If however it gave directions to add it to the food, then that should be okay.
You don't want to re-write the manufacturer's instructions.
I've always used straight Praziquantel. Where I buy it from:
National Fish Pharmaceuticals
http://www.fishyfarmacy.com/
I think has a minimum order requirement, but you can find other meds there, too. You might sure the Web on that word to see who else might carry it AND if it is a part of some other product that recommends feeding it to the fish.
I only know for sure that Praziquantel powder, mixed with wet food, fed directly to the fish in the quantity that matches the fish's weight (not necessary to miss any meals) works with one single dose, repeated 6 weeks later.