Ebo-jagger/cooler incubator fluctions

[Zoe]

Okay, I recently set up an incubator, heated with an ebo-jagger water heater in a cooler with some water, bricks and the tupperware. Now, the heater is on the highest setting, and I'm having two problems:

- The temp only reaches 83F max, and I want it to be able to hit 90 at least. What's the solution - a higher wattage? Less water?

- The temperature fluctuates by 1.5F... between 82.3 and 83.5 or something like that. What can fix that? More water? Less water? Insulating the cooler? New heater?

Thanks!
Zoe