Can I make a very important suggestion to you regarding the bioactive tank? I'll be up front and tell you that I'm totally against them for bearded dragons specifically, not all reptiles or amphibians, but certainly for desert ones because they are NOTHING like their natural habitat, which is only the Australian desert, because it is a very hard, rocky terrain with sparse vegetation. So keeping them in a bioactive tank is in my opinion very unnatural and actually very unhealthy as well, because bearded dragons are very prone to parasitic infections and bacterial/fungal infections (their natural habitats are much more "sterile" and you're introducing many microbes to his system that he isn't equipped to naturally fight")...That being said, that isn't my beef right now...
I have encountered this 2 times prior on this very forum, you can search the actual threads I'm talking about by just searching for "bioactive" in the search bar so you can verify what I'm saying. Both of these times the OP was posting because they had gotten their new baby bearded dragons within the past month, they were very young, at the most a month old, just like your little guy, and the reason for both posts by the OP's was that their babies refused to eat after the first week or so of having them, and they were getting dangerously thin, just as your baby is. And in both situations the OP's had put their new, tiny, young baby beardies into a large, cluttered, bioactive tank exactly like yours. And we as long-time members had to fight them about emptying the bioactive tanks out, completely disinfecting the tanks with very hot water and bleach or F10 disinfectant (along with everything else inside the tank that was going to be put back into the freshly cleaned tank), having them put down clean, dry paper towels as the substrate so that they could be simply thrown out and replaced as they became soiled, and then setting up the tank as a standard baby bearded dragon habitat with a Hot Side, Cool Side, a dedicated, main Basking Spot/Platform that was within the Hot Side and directly under both the bright white basking bulb and an adequate and unobstructed 10.0 UVB tube (must be mounted UNDER the mesh lid, as they block 40% of the
UVB light, and if using an 18" Reptisun 10.0 T8 UVb tube it cannot be obstructed by anything and must be within 6" at the farthest from that main Basking Spot), and having them recheck all 3 temperature zones with a Digital Probe Thermometer or a Temp Gun...
Now both of these cases were duplicate to yours in every way, and in both cases we finally did convince these 2 new members to ditch the bioactive tank, at least in a TEMPORARY manner, and in both cases their husbandry was actually okay as far as lighting and temps, it was just the extremely cluttered, overcrowded, and most importantly overwhelming bioactive tanks that were causing their young, new baby dragons to stress out completely and not eat, and in both cases their babies started eating the very next day. To the best of my knowledge at least one of these OP's did switch back to a bioactive tank, their decision, but not until their dragon was at least a year old. And I really believe that this is your issue 100%, your baby is in an extremely unnatural environment than what he is used to being in from his first month of life, but more impactfully from what he is innately meant to be in. Your Bioactive tank is too cluttered with junk and too overwhelming. Bearded Dragons like to hunt their live bugs, especially young babies and juveniles, even if that means nabbing a BSFL from off of the floor. But the bioactive tank presents numerous problems that a very young baby dragon just cannot handle, and this has been proven time and time again.
Your baby is extremely thin and doesn't look good, and my best and urgent advice is not to go out and buy a smaller tank, I have never seen tank size effect anything with a new baby, I have kept 3 month old babies in 40 gallon breeder tanks with excellent husbandry with zero issues. After all, think about their natural environment: dragons are solitary animals, and babies hatch and live alone from that point on, they don't stay together. They are alone in a vast Australian desert, so the tank size has nothing to do with it (assuming that your 3 temperature zones are within the correct ranges, your UVb tube is adequate, unobstructed, and within the correct distance of his main Basking Spot/Platform), but the Bioactive tank you have him in is not in any way natural to him or his species, and he's pretty new to begin with, and he has moved from a breeder to a pet shop, and now to you, so 3 moves, and now he's inside that bioactive environment that is just too much for him to take. He's completely overwhelmed and stressed, and he is not going to start eating on his own until he again feels comfortable and at home in an environment that is natural to him. And he cannot afford to lose any more weight at all, he's becoming emaciated and his eyes are starting to look sleepy and sunken as well. Remember that they also get most all of their
hydration from their live insects during their first year of life...
So my best advice to you is to immediately ditch the bioactive tank, dump it all out, completely disinfect the tank you have and the decor/bowls that will go back in it, then put down paper towels as a plain, simple substrate that will make his live worms and other live insects show up vividly to him, get his 3 temperature zones within the correct ranges and his UVB tube mounted unobstructed and within the proper distance from his UVB tube, and then be sure to keep both his UVB tube and his bright white basking bulb on each day for at least 13-14 hours. Put him back in his newly disinfected and uncluttered tank and allow him to acclimate a bit and warm up, and then throw 2-3 BSFL or whatever live insects you're feeding him on the paper towels, and I'm willing to bet that within 24 hours of being allowed to adjust in his new and more familiar environment that he will start eating like a little garbage disposal. But you need to do this quickly, as he needs to start eating a large amount of live protein every day pretty directly before he starts to become very sick and going downhill...you can always go back to a bioactive tank when he's an acclimated adult if you choose to, I don't suggest it and I don't condone it or endorse it, but that's your choice and I respect that totally, but right now it's obviously not working and you're going to run out of time to find out if I'm correct or not, and that's why I suggested that you search for the other very similar, almost duplicate posts to this one...