The major difference is actually a result from the volume, the 45 gallon cools quicker and easier because the total volume of water is lower. The 150 gallon will get most of the heat from the lighting but it takes more effort to extract that heat because of the higher volume. Try maintaining your 150 temp at 80F instead of 78F. This will increase the temperature gradient of the tank and the room and reduce the temperature gradient of the tank and the lighting, this will result in a lower overall temperature swing.
The pumps are adding little heat, experiment if you like by keeping the lights off one day and monitoring the temperature. Also try turning off one of the pumps in a separate experiment if possible.
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