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There isn't enough water running through the hood to keep the heater submerged. There's not enough room for the heater in the hood also. I have attempted to alter the bio-wheel filtration before to make the water flow less strong, but I ended up causing a small leak. It's a bit hard to do any type of modification to the Eclipse hoods. (For lighting, there are specific kits available to modify the stock lights.) But as for adjusting the water flow, I wouldn't recommend it.
A 25-watt Visitherm Stealth heater
would work out nicely in this tank. You'll have to put it in the tank itself but the heater is black and it won't be too noticeable once you get your decorations in.