I set up a 10 gallon tank for a quarintine tank. I used two 10 inch square plastic containers with soil and saf t sorb and planted about 20 baby Amazon swords. The tank cycled in about 5 weeks never having fish in it. I then bought 5 rummy nose tetras and 3 cardinals to increase the numbers in my main tank. About the fifth day (after not paying close enough attention to the tank) I noticed that they were all covered in ich. Lost all three cardinals before the second day of treatment. I've never had ich in all the years I've kept fish. My question comes after I went back to the LFS and what he told me. His explanation as to where the ich came from was probably from a drop in water temp which caused them to stress and become infected with ich. Temp in the tank from day 1 of setup with or without fish was 78°. If I understand what I've researched on ich, it has to have fish to survive. So one or more of the newly purchased fish would have been infected. Is this a correct assumption?