If you are looking for Internal Parasite meds, Prazi Pro i think is one of the goto meds for US members...
Just start with half dose first to make sure your fish dont react adversely to it...
Also, just as a heads up, 10-20% water change is really quite minimal, unless you are really under-feeding your puffers and water quality stays top notch...
Otherwise, normally a 50% or more water change is recommended, but again, if parameters are staying well below warning levels, then i guess the 10-20% could be enough for now...