well i just found out my heater in my 40 gal isn't working. from the looks of it the heater hasn't been working for a long time. i'm staped on cash for at lest 3 weeks. so i can't afford to buy a new heater. any ideas how to keep the water temp up for my 2 needlenose fish. i don't want them going into shock from the cold water and all. please let me know asap. been doing mini water changes since i found out it's not helping much