Well said by Venus, as you've got some serious husbandry and very serious diet issues, and I say this respectfully because you're trying to get help with it, and I appreciate that. His diet is completely inadequate for an adult bearded dragon, as is his UVB lighting. And you made no mention of the temperature gradient inside his tank. Part of the reason he is not eating anything but "junk food", i.e. mealworms/superoworms, is because of inadequate UVB lighting and most likely improper temperatures. Either way, you need to stop the mealworms completely, they are at best an occasional treat to be fed 2-3 a week, but there are better "treat" insects. He is very likely to end up with Fatty Liver Disease as well as MBD, so let's work on getting his lighting and temperatures corrected ASAP.
You can keep your 55 Gallon tank, it's narrow but doable, adult dragons do need at least a 40 Gallon Breeder tank, so you can make the 55 Gallon work, but either way you need to purchase A T5 strength UVB tube, as already stated by Venus. This is not optional for a Bearded Dragon. The
UVB light you have is not adequate even if he was in a tiny tank, let alone a 55 Gallon tank. Amazon.com is by far the cheapest place to order T5 UVB tubes because they will offer you a "Package Deal" that includes both the UVb tube and the Fixture for it.
I would order a Reptisun 10.0 (NEVER ORDER A REPTISUN 5.0), so a Reptisun 10.0 T5 High-Output UVB tube, which comes in lengths of 16", 22", and 34". The UVB tube needs to go across the entire Hot Side of his tank and then into the Cool Side of his tank, so you at the very least need to order the 22" Reptisun 10.0 T5HO UVB tube, and if you search on Amazon.com for it just as I just typed it in, you'll find a retailer selling this exact tube new for $23, which is a steal. If you click on the $23 retailer it will bring up the page for that exact 22" Reptisun 10.0 T5HO UVB tube, and then if you scroll down you sill see them offering a "Package Deal" with several different 24" T5-rated tube Fixtures to house the UVB in. DO NOT JUST CHOOSE THE CHEAPEST T5-RATED TUBE FIXTURE, AS YOU MUST ORDER ONE THAT INCLUDES A METAL REFLECTOR INSIDE IT!!! This Metal Reflector sits inside the tube Fixture behind where the UVB tube sits, and will reflect the
UVb light throughout the large tank. So choose the cheapest T5-rated (24 watts) tube fixture that has a Metal Reflector included with it. You should be able to get both the 22" Reptisun 10.0 T5HO UVB tube and a matching 24" fixture that is rated for a T5 UVb tube, 24 watts, with a Metal Reflector included, for under $50 shipped (yes, the 22" tube fits into a 24" fixture).
Also on Amazon.com, please order a "Digital Probe Thermometer), which should only cost around $5 or less, if you don't already have one, and you're only using stick-on thermometers. I don't know if that's the case, but I'm guessing it is. You cannot measure the Basking Spot Surface Temperature with a stick-on thermometer at all, and besides that they are horribly inaccurate, often off by between 10-20 degrees to the low-side when tested. So this is also not optional. You can also buy a Digital Probe Thermometer at any Petco or PetSmart for $9.99, but cheaper on Amazon.com when you order the new T5 UVB tube.
BASKING SPOT SURFACE TEMPERATURE (located within the Hot Side of the tank): Between 105-110 degrees for a baby or juvenile, and between 100-105 degrees for an adult over a year old. *****110 degrees is the absolute hottest temperature that should be anywhere inside a Bearded Dragon's tank.****
HOT SIDE AMBIENT (air) TEMPERATURE (side of the tank surrounding/containing the main Basking Spot/Platform): between 88-93 degrees maximum.
COOL SIDE AMBIENT (air) TEMPERATURE (side of the tank opposite the Hot Side): between 75-80 degrees maximum.
***Be sure to allow the Probe of the Digital Probe Thermometer to sit on each spot for at least 20-30 minutes each time before reading the temperature.
As far as his Basking Bulb, it should only be a Bright White Basking Bulb, and not any colored bulbs, like red, blue, yellow, green, black, purple, etc. You can either use a Reptile Specific, Bright White Basking Bulb, like the ZooMed Intense Basking Spot Bulb, or just a regular, household, Halogen Indoor Flood Bulb like you buy at Tractor Supply, Home Depot, or Lowes, the PAR38 Halogen Indoor Flood Bulbs. That's what most of use use.
****For most 40 Gallon Breeder Tanks, it takes a 100 watt Halogen Indoor Flood Bulb over the Hot Side of the tank to get all 3 temperature zones/gradient within the correct ranges, so for a 55 Gallon tank I would ry a 125 watt Halogen Indoor Flood Bulb first, that should work fine, and then you can adjust the BAsking Bulb up or down to tweak the temperature up or down a few degrees.****
PROPER LIGHTING SET-UP:
-You need to have a Hot Side of the tank and a Cool Side of the tank. His main Basking Spot/Platform needs to be located within the Hot Side of the tank. When you receive the T5 UVb tube it needs to be mounted under the mesh lid of your tank, as he is most likely suffering from a calcium deficiency and the start of MBD, and it's best to not have the UVb tube obstructed by anything. Some people allow their T5 UVB tubes to sit on top of the mesh as long as their Basking Spot/Platform can get within at least 10"-11" of the T5 UVB tube, but in this situation I suggest poking 4 holes in the mesh and then using either large, plastic Zip Ties, Shoelaces, Twine, Wire, etc. to attach the entire Fixture to the underside of the mesh lid.
-Both the T5 UVB tube and the Bright White Basking bulb need to both be over the Hot Side (the Bright White Basking Bulb can sit on top of the mesh lid) and be RIGHT ALONGSIDE EACH OTHER! You need to center the UVb tube and the Bright White Basking bulb so that they are both sharing the Hot Side of the tank, and then move his Basking Spot/Platform so that it's directly under both lights, so he gets both lights at the same time while basking. This is replicating natural sunlight for him. Both of these lights need to be on every day for at least 13-14 hours.
-Be sure that the Basking spot/Platform is always within at least 10-11" of the T5 UVB tube. You cannot raise the UVb tube or lower the Basking spot/Platform away from each other to adjust the Basking Spot temperature or the Hot Side Ambient temperature, you can only move the Basking Bulb.
-If by chance the single, higher wattage Bright white Basking bulb that is over the Hot Side of the tank does not get the Cool Side to at least 75 degrees, then you may need to add a second Bright White Basking Bulb over the Cool Side in a Clamp Lamp or another Dome Lame, but it will only need to be a much lower wattage of Halogen Indoor Flood Bulb, usually only a 30 watt or so will do it. You may not need one at all, you just have to measure the temperatures once you get the lights set up correctly.
PROPER DIET:
First of all, an adult dragon should get a large, fresh salad of appropriate, healthy greens every single day, which include Collard Greens, Mustard Greens, Turnip Greens, Dandelion Greens, Escarole, Endive, Swiss Chard, Bok Choy and Pak Choy, and Arugula/Rocket. Try to avoid all types of Kale and Spinach, as they both contain very high amount of Oxalates, which will bind to all of the Calcium he eats, and then he will just excrete all of the Calcium he eats out and not absorb it (this is how people get Calcium Oxalate Kidney Stones). You can also add healthy, fresh veggies, the good ones are any types of Squash (Butternut, Spaghetti, Yellow, Green, Acorn, etc.), Bell Peppers of all Colors, Green Beans, Peas and Pea Pods, and a little Broccoli and Carrot. Fruit should only be given once or twice a week at most as a treat in small quantities, as it contains a very high amount of sugar. NEVER FEED ANY CITRUS FRUIT. So he needs to get this large salad of appropriate Greens and Veggies every single day.
You need to also feed him healthy, LIVE, staple insects at least 2-3 times a week, and give them to him in the morning before you give him his salad. You are much better off money-wise to order your LIVE staple insects online in bulk than buying them in a pet store, which is ridiculously expensive. You can keep them in a big, plastic tub, like one you buy a Walmart (50 Litre works well), and you should gutload the insects with the exact same greens, veggies, and fruits that you feed him, once every day just throw in few greens and veggies into their bins.
Proper live, staple insects for Bearded Dragons include Crickets, Several different species of Roaches, BSFL/Phoenix Worms/NutriGrubs/Reptiworms/Calciworms (all the same thing), and Silkworms (these must be fed either Mulberry leave or Silkworm Chow). The cheapest places online that I've found for most insects are
www.dubiaroaches.com (they have all types of insects) and
www.symtonbsf.com Amazon.com has live Silkworms available, but in small quantities.