I can think of two big reasons not to treat for chytrid without evidence. The first is that man-handling the frog is stressful. The second reason is more serious - the fungicidal treatments people use have not been investigated properly for amphibians. While they don't appear to have negative effects, from a treatment point of view this is a brand new disease and people are using chemicals, designed for different applications, to treat animals that are the most sensitive vertebrates to any chemicals that come in contact with their skin. I would not put my pet at risk unless I had determined chytrid was involved (which can be properly tested for, for relatively little money).