Well... what I do is the next.
Here in Mexico, there are two types of brine shrimp you can usually find. One that is cultured at home by someone who sells it, and one that's captured (I don't know where for certain, but OK...). I always try to buy the one that's cultured because the other one usually has parasites that can affect the fish. So, what I do (it was suggested to me by a friend of mine who owns a fish store and really knows a lot about fish) is take a syringe of 3 ml, fill it with just a little, well, here it's called "desparasitante" but I believe such a word doesn't exist in English... so, it's the liquid we humans drink every year or so to kill the parasites we may have inside. That done, I use 2 drops maybe 3 on 1lt of water. I then put some live brine shrimps to swim in the water for 15 minutes or so, they'll absorb the "desparasitante" and then I give them to the fish. I do it every 6 months and haven't suffered, so does my friend, of any parasites in mi fish and I surely hope it keeps this way.