I have two thermometers in the same fish tank. One of the thermometers reads in Fahrenheit and one in Celsius. Keeping a temperature about 79-80 degrees Fahrenheit, this would convert to a Celsius reading of 26.1-26.67. However using a Celsius submersible thermometer this reading was 28 plus degrees. Thinking that the thermometer could be a defect I used several other Celsius thermometers only to get the same result. I purchased an inexpensive thermometer with probe able to switch from Fahrenheit to Celsius. The readings seemed to be in line with the conversion table. ( 79 was 26.3 80 was 26.9 ) Anyone know why the Celsius thermometers give a reading about 1 degree higher?