My bearded dragon has a small lump on its tail and I'm not too worried because it's pretty small but better safe than sorry because I am very new to this.
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Well you definitely need a uvb light. a REPTISUN 10.0 T5 tube is what you need along with a bright white basking light. I use halogen flood bulbs. How big is the enclosure? If you can post a picture of his enclosure that would help and a picture of the lights. Unfortunately mbd is not curable. You can with proper care keep it in check. Also besides the uvb he needs calcium his feeders should be dusted at least 3x a week.
Yep unless that bulb is a mvb those put off heat and uvb which I'm thinking its not. That's how he developed Mbd. You need to get the reptisun 10.0 Tube t5 ASAP. If you look to the right there are care sheets on lighting. Hopefully you can get the bulb and calcium so he won't be come worse. That's why he's so dark to not only will he perk up once you get the uvb his co!ors and appetite will also imrove.
Also - looks like you have some kind of woodchips or gravely sand in there .... VERY BAD FOR BEARDIES ....recommend you remove the current bedding urgently and replace with either
>> paper toweling
or
>> loosely laid floor or wall tiles