Please do not listen to the pet stores -- they usually give bad advice and most do not know what they are talking about-- first you need a good UVB and for the size of your tank I would recommend and 24" fixture w/ reflector like this
https://www.pangeareptile.com/store/zoo-med-reptisun-t5-ho-terrarium-hood.html the Reptisun is out of stock so please get this one its actually better than the Reptisun one get a 22" and these are in stock the Reptisun one is out of stock now these need to be changed out once a year I recommend the month before --- Depending on the screen on your tank would determine where the UVB needs to go -- if the screen is a wide hole type it can sit on top if its a fine screen like a screen door it needs to go inside the tank w/ basking distance 12-15 inches directly above the basking decor- he needs to be able to sit underneath - for a wide hole 8-10 inches w/ basking decor directly underneath
Please get rid of the sand --tiles are great for substrate please get a slated ceramic tile so he does not slip - they can be layed in the tank loose w/ a thick shop paper towel underneath to catch the watery urate -- easy clean up w/ vinegar/ water 50/50 solution - I tiled my 4x2x2 for $13 --
Please get rid of the heat mat dragons heat from their backs not stomachs -- a CHE is only needed if the tank is dropping below 65 at nite and not over 75 -- dragons like it cool and dark - your basking bulb needs to be able to keep temps 95-110 for adult and that temp needs to be taken w/ a digital probe thermometer taken where he sits for basking -- NO stick ons please they are inaccurate- you should have 3 temps in the tank basking 95-110 middle of tank 90's and cool side of tank 80's - he needs more climbing decor please -- you can look outside for logs branches etc they would need to be baked before using to kill whatever is living inside or you can look at Pet Smart for some really nice decor for dragons --they are easy to keep clean
As far as the
black beard it could be from improper temps in the tank incorrect UVB - its not real dark but he is in some distress-- you dont want it going pitch black - the two most inportant things in the tank are the basking temps and good UVB - that is going to control his overall health and behavior- its great your switching him off the pellets etc and fresh greens are the best for him along w/ a good staple insect here is a website for nutrition ignore the kale thing its a good staple feeder
http://www.beautifuldragons.com/Nutrition.html
If you need anymore help please ask -- I would get your temps and UVB straightened out and see if the
black beard goes away
Karrie