I have a 20 gallon long tank for my ball. I bought a 40 watt and 60 watt ceramic bulb. The problem is the 40 watt will keep the tank at about 80-85 with a basking spot of about 90. The 60 watt will keep tha tank about 90-93 witha basking spot of like 98-100. All of this is fanenheit(spelling?). My qestion is do I use the 40 or 60 watt bulb??? I also have a small under tank heater as well. Thanks.