You need a minimum of 8 weeks to kill ich with no host and preferably 12 weeks and even this may not kill it. I've battled it for a year and ended up tearing down my tank. Raise the temp to 82-84F, the higher the better and remove all your fish for 8-12 weeks. Try to keep the lights off as much as possible too. Treat all your fish with copper which is the only effective treatment. And make sure you get a copper test kit that is the same brand as your copper treatment. Just check out all the failures posted at Wetwebmedia, Aquarium, Pond, Marine and Freshwater Fish, reef tanks, and Aquatics Information This is a bad disease and very difficult to eradicate. All your new fish should have a FW dip and QT for 2-4 weeks. I now treat all my new fish with low level copper. And I dont buy any more live rock. I use dead rock and live sand. Good Luck!