Yeah, the Reptiglo is a weak T8 tube that is only good for at most 6 months, after that it won't be emitting any
UVB light at all and needs replaced. The cheapest, easiest way to do so is to buy an 18" or whatever length you currently have Reptisun 10.0 T8 UVB tube, it's 2 watts stronger than the Reptiglo and emits no harmful rays. It does have to be mounted underneath the mesh lid though, as did the Reptiglo, soI really believe that's your main issue here, a lack of
UVB light.
That mesh has been blocking 40% of the UVB/UVA light from the Reptiglo tube, which is far too weak to be blocked, and if it's older than 6 months old (I believe you said 8 months old) then it's not emitted any adequate
UVb light for awhile anyway. Realize that if a T8 strength UVb tube is not strapped to the underside of the mesh lid and within at least 6" of the dragon, then the dragon has not gotten any adequate
UVb light, and therefore has not really been absorbing, processing, or able to use any Calcium or any other nutrition (vitamins, minerals, etc.) from the food or any supplements that you've given him.
In addition, this will also cause severe digestion issues, which in my opinion is why the he has runny stools, and I believe this because of him passing a whole wax worm. No, he didn't pass the wax worm "alive", the stomach acids kill them immediately, but they come out whole for 2 main reasons, #1) Improper temperature zones (too low, specifically the Basking Spot Surface Area not being at least between 100-105 degrees F), and #2) Inadequate UVB/UVA light for at least 13-14 hours every day.
I would hold off on the vet for right now, and instead immediately replace and upgrade that UVB tube with an 18" Reptisun 10.0 T8 UVB tube, it will fit into the fixture you already have since they are both T8 UVb tubes, but the Reptisun 10.0 is stronger, more intense, and a better overall tube. Plus, the 10.0 emits 60% UVA light in addition to the
UVB light, I don't know what the Reptiglo tube emits but I know they are far weaker. I would run to Petco or Petsmart and get the Reptisun 10.0 (not 5.0) immediately, and then poke 4 holes in the mesh lid over the Hot Side of the tank, being sure to leave room for the Basking Bulb to sit right alongside the UVB tube, so that both lights are "sharing" the top of the Hot Side of the tank, then position his Basking Spot/Platform directly under both lights, so that he gets both at the same time while basking. Be sure to leave both lights on every day for at least 14 hours.
FYI, the 18" Reptisun 10.0 T8 UVB tube has a retail of $37.99 at Petco and Petsmart, but at least at Petco (I'm not sure about Petsmart) if you go onto the Petco website and look up the Reptisun 10.0 T8 tube it costs $18, so just look it up on your phone and keep the page up, then take the tube and your phone to the register, tell them you have a website price match, and they'll sell it to you for the $18 on the spot...
After you get the new UVB tube fixture strapped to the underside of the mesh lid and the basking spot/platform directly underneath both lights, and ensure that the basking spot/platform is within at least 6" of the now unobstructed UVB tube, then use your Digital Probe Thermometer to measure the temperature of the Basking Spot Surface area. Be sure to let the Probe on the basking spot/platform for at least 20-30 minutes before reading it. If it's not between 100-105 degrees F, then you need a higher wattage bright-white colored basking bulb.
I really think that once you get him under a strong, adequate, 10% UVB tube that is unobstructed by the mesh lid and within 6" of his basking spot, and you get his basking spot/platform between 100-105 degrees F using a bright-white basking light (and not just a CHE), all of these issues are going to fix themselves very quickly.