The CopperSafe says it’s good on Ick, Flukes, Anchor Worms, Velvet “and other external parasites.” It is stable in your water for 30 days (of course, do not be pulling it out by running carbon or anything like that). So, you can start with your ‘old’ tank water, if you’d like, a new batch of saltwater, or any combination to fill your tank and pour the teaspoons of CopperSafe into initially (as you dose-up to the therapeutic level over a few days). This is because if all goes as it is supposed to, ‘none of the above’ listed problems will survive 30 days of therapeutic-level CopperSafe. After 30 days, just replace with non-medicated water (or run carbon) to pull down (and out) the CoperSafe. From there, continue to use your hospital tank for another 30 days to observe your fish before returning it/them to your display tank. Also, if you need to use additional medication for things not treated by CopperSafe, your tank has a fairly clean re-set. But again, you will have to watch your ammonia levels throughout (again, the SeaChem ammonia badge), because you basically have fish in an uncycled tank. Lastly, they may be in there 12 weeks if you need to let your display tank go fallow past all Ick possibilities. None of this is as hard as it sounds; but the smallest volume of water you can get away with, the smaller amounts of water to change out.