Put the temperature right up.
If there are parasites they should hatch and live out their life cycle muchg
better.
remember parasites are only a problem if the environment favours them over
fish.
Ensure your water is good (0ammonia, 0nitrite less than 40ppm nitrate) and
you will be surprised at what continue to live healthily.
Often some high quality fish food like spirulina flakes, frozen brine shrimp
or the like will keep fish far healthier than medications.
And always they regular partial water changes.
Always a reason behind parasite outbreaks, but without a microscope your
blind even to the species.... they are all very different.
Kill your snails if you have any.