I've had some success in clearing my puffers of parasites by adding garlic extract to their food. I buy concentrated garlic extract from GNC. I add about 2 drops per teaspoon of food (thawed shrimp, FD Krill, food sticks, etc.) and let the extract soak in for a short time (no exact time but, more than 10 minutes). Then feed it to my fish. The extract infused foods appear to have improved new fish appetites and definitely cleared my new puffers of intestinal parasites in just a few days.
I know some people that feed chopped raw garlic directly to their fish. But, my fish are too big to rush at small chopped foods. I know a few people that swear by the use of garlic powder. I tried it since the powder is cheap but, all it did was float to the surface of my tanks and generally just result in cloudy water with a garlic smell.
The extract I get is labeled 'odorless'. There's only a slight odor if you sniff the bottle directly. The fish tanks no longer smell of garlic.