Thank you for getting back to me, Bridget. It's possible your skink is hibernating, but we don't want to assume that unless all conditions are perfect for him. I'm going to start you out with a first aid measure that you can take right away. This will help no matter what is wrong. Buy some Dioralyte (yes, the kind for human infants), and prepare a shallow warm bath consisting of 1/2 warm water and 1/2 Dioralyte. Soak your lizard
for about 20 to 30 minutes. Be sure to supervise closely. Repeat these soaks twice a day.
It's important to get a thermometer so you can measure the temperatures. The cool side should be at about 23*C. The ambient air at 29*C, and the basking area at 33*C. Having this temperature gradient allows the skinks to choose where they are most comfortable at any given time. A skink that doesn't have a warm enough basking area will lose its appetite and even become sick.
I'm not sure you ahve a UVB light at all. UVB bulb size is measured not in volts or watts, but in percent output, for example 5% or 10%. The only information I could fine on the light you mentioned is that it is a heat lamp. UVB lights don't put out heat - they are cool tot he touch. If you don't have one, it's extremely important that you buy an additional light that produces UVB rays. A Reptisun 10.0 is a good brand that does. If you choose another brand be absolutely certain it provides UVB rays. Don't take the word of pet store personnel, but read it for yourself. Full-spectrum, DayGlo, daylight, UV, and UVA are NOT the same thing. I'm putting a lot of emphasis on this because it's crucial to a reptile’s health. Without this light, Metabolic Bone Disease (MBD) will develop because they won't be able to produce vitamin D. Vitamin supplements are not a good replacement for the proper lighting. MBD causes a very slow and painful death. UVB bulbs must be replaced every six months as they lose their effectiveness after that, even though they may still look fine. Light that comes through a window isn't sufficient because the glass filters out the UVB rays.
After your skink has a couple of soaks and has been warm enough for several hours, try feeding him. If he doesn't seem more active, and still won't eat, you'll have to make a decision. It's extremely difficult to tell if a lizard is sick or if it is hibernating. If we assume hibernation, the lizard can die if that's not the case. For that reason, I prefer to have an inactive lizard checked out by a reptile vet. If you decide to do that, this link will take you to a directory of such vets in Australia:
If you have more questions, let me know in a REPLY. I hope your skink will perk up and eat after a couple of soaks and warmer temperatures.
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