Hello. Am experiencing some sad times w/ my 29 gallon tank. Came on rather suddenly. Have lost two black tetras and one serpae tetra. Heater is turned up as high as it will go, but thermometer is only about 72 degrees F. Fish will NOT eat anything. :sad am going to try another 1/4 water change and see if this remedies the problem. Also have some live plants: Amazon swords