I use New Life Spectrum Thera+A which has more garlic than their other formulas, enough to kill some parasites.
Garlic has been scientifically shown to kill some parasites, but the form is very important. The liquid additives at the LFS will help get fish to eat, but won't kill parasites. The best thing for that is the juice from freshly pressed garlic. Soak the food in that juice and you have a great garlic enhanced food.