I had some Mollies that died from either ich or a fungus. I did multiple water changes, treated with heat and salt, but both died anyway. I waited about a week after the second mollie died before moving 2 of my guppies into that tank. The guppies look good and healthy, but I am wondering if there is an incubation phase with either ich or fungus. If they were going to get sick from the tank, wouldn't it have happened by now? They have been living in that tank for a couple weeks now with no signs of disease.