A hole in the center would let light in would it not? Mine has the pump in the tank too but I use the VIA 526 gph pump. It does produce some heat but my experience is it only adds about 3-5 deg F. You can cool the water with several things.

As lakewood said a vent hole is always a good idea as long as water does not get out or light get in.

Concrete will drop the temp some. What works well too is the miracle thaw. You can find them at garage sales, swap meet and even the 99ΒΆ store sometime. You may need 2 of them but they will draw some of the heat out the water.

However you do it you need to get the temp down cool water will hold more oxygen then warm water will. Keep the light out of the water alga is not good for root growth.

The idea behind anti-wilt is to replace the humidity dome and keep the cutting from drying out under the lights so it has a chance to root.