Well that solves the mystery, you have an 18" Reptisun 10.0 T8 UVB tube, which is not providing him with any adequate
UVB light at all because it's on top of the mesh lid. It makes no difference how close he is to that mesh, it is blocking about 40% of the
UVB light emitted by the tube from getting on the other side of the mesh, and it's far too weak a UVB tube to have nearly half the
UVB light blocked. This is EXACTLY why he's so sick, he's not been able to absorb much, if any Calcium that he's been taking in from his food or supplements, and his MBD is very advanced as a result of this. This is why he has no appetite and is extremely lethargic.
The good news here is that #1) It's an easy fix, and #2) You can use that Reptisun 10.0 UVB tube AS LONG AS YOU FOLLOW THE RULES FOR A T8 UVB TUBE VERY, VERY CLOSELY....This is not optional, as you can see by how bad-off he is right now. The Reptisun 10.0 T8 UVB tube is a very good UVB tube for a Dragon, BUT IT'S COMPLETELY WORTHLESS IF YOU DON'T HAVE IT MOUNTED CORRECTLY OR WITHIN THE CORRECT DISTANCE, AND IT'S NOT REPLACED OFTEN ENOUGH.
********ONE THING I FORGOT TO ASK YOU TO CHECK, JUST IN CASE THAT IS EXTREMELY IMPORTANT....Is there any kind of clear, plastic cover on the bottom of your tube fixture that is covering the UVB tube inside it? Some fixtures come with these damn "Safety Covers" in case the person decides to use them for a heat tube, but unfortunately NO STRENGTH OF
UVB LIGHT CAN PENETRATE ANY GLASS OR CLEAR PLASTIC AT ALL, IT BLOCKS 100% OF THE
UVB LIGHT! So please check your tube fixture and make sure that there is no clear, plastic cover over the UVB tube. If there is, it's been blocking ALL, 100% of the
UVB light and he's gotten none, and you must remove it immediately.
The very first thing that you need to do IMMEDIATELY, RIGHT NOW, is get that UVB tube/fixture strapped to the underside of the mesh lid. You can easily do this using long, plastic Zip Ties, Wire, Twine, etc. The mesh on those Exo Terra lids is very fine, so it's actually probably been blocking more than 40% of the UVB, I have the same tank but it's not as tall as yours, and the mesh is very, very fine. If you're able to weave the Zip Ties, Wire, Twine, String, etc. through the holes in the mesh, then that's the easiest way to do this. If not, then you'll have to use a Utility Knife or Shears to poke some small holes in the mesh to put them through. Then you just have to strap the entire tube fixture to the underside of the mesh lid. BE SURE THAT YOU ARE SETTING YOUR LIGHTS UP PROPERLY WHEN YOU'RE DOING THIS!!! You must have the UVB tube strapped to the underside of the mesh lid on the Hot Side of the tank, leaving room for your Basking Bulb to sit right alongside it, both sharing the top of the Hot Side of the tank, with his Basking Platform/Ramp directly underneath BOTH LIGHTS...Do what you have to do here to keep his Basking Spot Surface Temperature around 105 degrees F, this is also NOT OPTIONAL, as the Basking Spot Surface Temperature determines whether or not he can properly digest any food that he eats, and thus whether or not he absorbs any nutrition from the food. Having an Ambient/Air Temperature across the tank of about 80 degrees is perfectly fine, don't worry about that at all, it's the Basking Spot Surface Temperature, the spot where he lays and THAT IS WITHIN AT LEAST 6" OF THE NOW UNOBSTRUCTED T8 STRENGTH UVB TUBE, THAT MUST BE AROUND 105 DEGREES F.
******So here's your rules for a T8 UVB Tube, and they must be followed EXACTLY, otherwise you see what happens:
#1) A T8 UVB tube can NEVER be obstructed by anything at all, like a mesh lid to the tank; there must be NOTHING between the BARE T8 UVB TUBE and your Dragon on his Basking Spot!
#2) A T8 UVB tube must be at least WITHIN 6" OF YOUR DRAGON in order to deliver adequate
UVB light to him. So after you strap the tube fixture to the underside of the mesh, please measure the distance between the actual bare UVB tube inside the fixture (assuming you've removed any clear, plastic cover if there was one) and the spot that your Dragon is going to be laying on while he basks under both lights. This distance must be no greater than 6".
#3) All T8 UVB tubes MUST BE REPLACED ONCE EVERY 6 MONTHS ON THE DOT!!! T8 UVB tubes have a very fast
UVB light decay-rate, and as a result after 6 months of use, they are basically emitting little to no
UVb light at all; They will still turn-on and light up, but they are only emitting UVA light, no
UVB light. So you absolutely must replace them once every 6 months. I recommend writing the date you first start using a T8 tube right on the tube itself with a Sharpie, that way you'll be sure to know when it needs replaced....
****You may want to think about upgrading both the UVB tube and the tube fixture w/reflector to the much stronger T5HO Reptisun 10.0 tube. Yes, you have to replace both the tube and the fixture, as the fixture you have is not rated for a strong T5 UVB tube....Here's the difference, and this should show you why your Dragon is as sick as he is...The 18" Reptisun 10.0 T8 UVB tube you have been using is only a 15 watt UVB tube...The 22" Reptisun 10.0 T5HO UVB tube is 24 watts...
#1) A T5 UVB tube can sit on top of a mesh lid to the tank and still penetrate adequate
UVB light to your Dragon (in the case of your Dragon, if you are to upgrade to a T5 UVb tube and fixture anytime soon, I'd still strap it to the underside of the mesh lid for him for the first year of having it, as he needs a lot of strong, direct
UVB light for the foreseeable future).
#2) A T5 UVB tube only needs to be within at least 10"-11" of your Dragon's basking spot/platform rather than at least 6", so the T5 tube gives you a lot more leeway with the height of your tank.
#3) A T5 UVB tube only needs to be replace once every 12 months, so you save a fortune over time from having to replace the T8 tube every 6 months.
Just as an FYI, the cheapest place to order a 22" Reptisun 10.0 T5HO UVB tube is on Amazon.com, the tube costs about $25 shipped, which is less than the T8 costs in a pet store. And Amazon.com also sells one particular 24" T5-rated tube fixture THAT INCLUDES A REFLECTOR WITH IT for around $28 shipped. (they have cheaper 24" T5-rated tube fixtures, but they don't include a reflector, and this is not optional). So for about $60 shipped you can upgrade. For now let's worry about getting that T8 tube under the lid.
****Whatever you are feeding him in the syringe, YOU MUST BE PUTTING BOTH A REPTILE GRADE CALCIUM POWDER W/D3 AND A REPTILE-GRADE MULTIVITAMIN POWDER IN IT!!! He will be able to start absorbing the Calcium and other nutrition as soon as you get that T8 tube strapped under th mesh lid and within at least 6" of him, so it's very, very important that he's getting Calcium with Vitamin D3 every single day for the next few months and a multivitamin I'd say 4 days a week. After he starts eating on his own and the Calcium Deficiency and MBD start to reverse themselves, then you can scale back the Calcium to 5 days a week for the rest of his life, and the Multivitamin for 3 days a week for the rest of his life...But for at least the next 3 months he needs a Calcium supplement every single day and a Multivitamin 4 days.