Marineland is a giant as far as mass produced aquarium supplies go, but that heater should not be that off the mark. Try re calibrating it, by un-plugging it,letting it cool off while still in the tank for say about 30 min. then remove it from the tank & let it sit at room temp for about 30 min.While still out of the water manually adjust the temp by adjusting the dial slowly to as low as it can go, then slowly adjust the dial to as high as it can go, then slowly back it down to the temp that works for you. Now place it in your tank DO NOT plug it in yet, wait for 30 min. then plug it in refrain from adjusting it and observe it for several hours, it should come on when the tank temp is less than what you set it to
be sure to keep it UN -plugged while it is out of the water even while you do the adjustments.
Last edited by paloverde; 11-11-2012 at 07:08 PM.
Reason: brain cramps.