For a 20 gallon tank a 75 watt should be good but you MUST have a digital probe thermometer to get the temp - 105-110 no hotter---- place the probe on the basking spot of where he sits 10 min then get the temp ---- NO coils for a UVB -- they are inadequate ---- you can use a long fixture usually a 18 or 20" T 8 I recommend a 24" fixture that comes w/ a 5.0 bulb which is equivalent to a T 8 bulb -- you will need to upgrade that tank to a 40 + gallon tank I recommend a 75-120 gallon but either way the 24" fixture would go right into a bigger tank you would need to upgrade the bulb to the T 5 at that point
