Hi Laura,
Thanks for taking Alf in, do you know how old he is? That is a huge tank for a dragon and not easy to heat and light. He needs a
UVB light (full-spectrum sunlight), that's very important. And the basking temp would be different depending on his age. There's a great
care sheet that covers all that on here, to the right, and the Newbie's guide to Lighting help is great info.
Mainly you need a good tube
UVB light that covers at least 3/4 of his tank, which means a long one in your case. It needs to be inside his tank about 8" from his basking spot along the back of the tank. I can't tell you how to mount it inside, as I use a different kind of light (see next paragraph). I use 40 gallon breeder tanks, a bit smaller of a tank, easier to heat & light. They're 3' long by 18" high by 18" wide, but then if he's an adult, the one he has gives him lots of space to run around.
The best type of thermometer is either a temperature gun or an Accurite digital temp guage with probe (I think you get these at any garden centre at Walmart, Lowes, like that). The temp gun would be more accurate. You'd want to use it on the basking spot (what is he using for the basking spot and how far is it from the mesh top?). I use mercury vapour lights in deep domes on lampstands, so don't use a mesh top. Maybe you could send me a picture? And I can send you a picture of my set up, too, if you'd like. Once all that is figured out, the rest is easy
As for temps. Depends on their age. If he's over a year old, then 100F to 102F is fine, if he's younger, then 105F would be fine. So let me know his age.
What is he eating and is he getting supplements? He should be getting his bugs dusted with a good calcium without phospherous (RepCal has a good one with a pink label) and also any type of vitamin/mineral powder. If he's over a year old, then 3 meals of bugs a week should be dusted with calcium, 1 meal per week with the vit/min. This is very important because they don't make their own calcium (like us) and needs it to develop strong bones. The vit/min is also necessary as they don't get everything from their food. He should also be getting greens, veggies. Here's a great list of food for dragons
http://www.beautifuldragons.com. If you check out their store, they sell a good temp gun, but you can also get one in pet shops (more expensive).
They don't need any light at night. If your house is less than 65F at night, then a ceramic heat emitter is best, heat without light. They need dark at night to sleep properly.
Not sure if I covered everything but would need more info on Alf, his age, weight, what he eats, etc to figure out if anything is missing.
One more very important thing, they need warm baths, at least 3 a week, for
hydration. Warm water and soak for at least 20 minutes. I soak mine every 2nd day (I have 5 dragons, 1 female, 4 males). Even if Alf eats lots of greens and veggies, he still needs baths. Dragons soak water up thru their vent. Their skin should be supple (meaning if you pinch it, it goes back into place). It's very important for their health.
So congrats again and get back to me about what you might need to know more about. And welcome to our forum!
Deb