Fish Reared in Hard Water are More Susceptible to Columnaris Disease / June 23, 2015 / News from the USDA Agricultural Research Service Read the magazine story to find out more. Catfish raised in hard water with high levels of calcium and other minerals are more vulnerable to columnaris disease, according to new ARS studies. Click the image for more information about it. Killing Fish Egg Fungus with a Disinfectant Using Clay to Fight Fish Disease Detecting and Preventing Disease in Trout Fish Reared in Hard Water are More Susceptible to Columnaris Disease By Sandra Avant June 23, 2015 Water hardness can influence the development of columnaris disease in catfish, according to a study by U.S. Department of Agriculture (USDA) scientists. Agricultural Research Service (ARS) scientists found a difference i...