i m using a threometer which sink at the bottom of my tank, i usually hide it at the corner. n the water temp. is always hothothot 81-83F . n i m having tiger barbs (68 to 79 F) , platyz (64 to 76 F) i wonder, should juz put an ice pack to cool down the water temp... will it be too cold at the surface but warm down the bottom, which make my fish frozen (tooo cold) ? :-/