I think this problem should be much simpler, given that the infected fish is a Porcupine Puffer. This fish tolerates freshwater baths better than any fish i have ever seen. You can easily dip 2 or 3 times per day for 1 minute at a time. The parasites, regardless of which type, will not tolerate the change in salinity and you should have a non-infected puffer within days. Combined with a hyposalinity treatement (1.015+) you will probably have a fully cured fish in 3 weeks.
For the record, feeding garlic has proven essential to boosting the immunity system of puffer fish. Avoid krill. You can reference
or any works by Kelly Jedlicki, who has become recognized as the foremost authority on pufferfish in the industry.