I just got the aqueon 29gallon deluxe kit. On the heater that came with it(all glass AGA100) the light comes on for a few seconds and then turns off for a few seconds. The only time it stays on longer is when I have it turned all the way up. Is this normal? I left it running in the middle position like the instructions said(which is supposed to be 75-79f) but it barely got to 70. I adjusted it up and let it sit. The highest Ive been able to get it is 72f(about half way between middle setting and max). Did I get a defective heater? any recommendations for a replacement?