Ick is caused from stress. Stress is caused by alot of reasons in a fish tank. Keep the water quality good, temperature steady, salinity,have enough hiding places,add compatible fish, don't overcrowd, just to name a few and you could still get ick, but your chances are much less. It's also very helpful to have a quarentine tank. When you do add a new fish turn the lights off for at least 3 hours for fish to get accustomed to the tank. Especially if you have other fish already. I would wait at least 6 weeks if you had a wipeout and then add 1 fish at a time very slowly, like maybe a month apart.