It's a trade off with good water quality and properly quarantined fish shouldn't have an ick problem.....but it can happen, but usually it's introduced or stress will trigger it......Again fish do better in the lower salinity levels, but if you have a reef with fish, you'll want a higher level such as 1.025 or 1.026 for your corals....they do better at that level than lower, so it's a trade off I guess.