Heater Problems Need Help!!?

i have 29g tank with 6 platy,3guppies, and few mollies. I have a tetra 100watt fully submersible heater. It came with my tank. It's been running for 5 months. My water has been at 76deg, but the water feels cold. The heaters has no knob to adjust. It automatically adjusts to 76-80deg. Is there a better heater? and recommened temp for fish. And is there water cold or warm when it is at 76dec. I have one of those strip thermometer, and it tells me 76 but i think it's at 72. And will my fry die around 76deg or do they need higher temp. PLZ HELP!!!