Please get rid of the sand , if he ingests it and can't get rid of it in his poo, IT WILL KILL HIM . No iffs , no buts.
We are not telling you this for our collective healths' , death from impaction is a horrible long and excrusiatingly painful way for a beardie to die. We see beardies keepers coming here with monotonous regularity in panic because they have a beardie who is impacted and even impacted beardies on death's door , often hoping for a cheap, quick, home remedy, often too late to save the bearded dragon.
About his going off his worms .
Firstly - how old is he ?
Secondly what is his body weight ?
...... recommend weighing him regularly (weekly say)?
If he is under 12 months old superworms are not a suitable feeder insect because
>> they have a very hard to digest exoskeleton that can block the intestines of a young bearded dragon and cause very serious impaction.
>> they have very high fat content
>> their Ca/P is very poor
They are at best treats only for an adult beardie (maybe 2 worms once or twice a week).
The fact that you have sand as your substrate and are reluctant to get rid of it indicates you've received very bad advise from someone.
So this is a RED FLAG for me.
Think it's a very good idea to quiz you on your husbandry and about your beardie's setup
We need details of your feeding schedule and other husbandry aspects to diagnose why beardie is off his food.
Might be a very easy fix .
Photos of the tank and showing substrate and lighting and of the beardie will help too. Use XIMG button to upload photos from your computer.
Can you give us a good rundown on the setup and schedules (light and feeding) :
Basking light
........ is it a coloured globe ? (BAD)
........ what is it's wattage ?
........ how far from the basking spot ?
TEMPERATURES ?
>>> daytime
.......warm zone
.......basking spot
...... how are you measuring your temperatures ?
TOO COLD = SLEEPY DRAGON
>>> overnight minimum viv temperatures ?
UVA AND UVB ADEQUATE ?
>>> is the uv rated AT LEAST 10%UVB ?
>>> is it a COMPACT (curly globe & WATTAGE ?
>>> or a T8 tube ?
>>> or a T5 tube ?
>>> or an MVB ?
VERY IMPORTANT : what is the brand ?
(not all UVB compacts and tubes are created equal or as well , many shops sell their own brand (Zilla, All Living Things, Reptile-One, Nat Geo , Natural Selections (in green boxes) which are cheap Chinese clones made very cheaply using very poor quality quartz glass and cheap phosphors ==> very poor UV spectrum produced incl UVC band and bad parts of the UVB band)
>>> also is it covered (in a domestic fluorescent light fitting )? == BAD
>>> also is it sitting ontop a mesh top ? == BAD
>>> how far from basking spot ?
too far and the UVA and UVB WILL BE TOO DILUTE.
UVA FLUX TOO LOW where dragon is ==> a very lethargic dragon w/ a very poor apetite just in the short term , and neurological problems if this persists , not to mention MVB if UVB flux too low long enough with inadequate metabolisation of dietary calcium or inadequate intake out calcium
TANK
>>> size (L x W x H) and construction , photos of the setup are often helpful .
SUBSTRATE ?
>>> is it sand ? == BAD AND IF CALCISAND this is EXTREMELY BAD/LETHAL when ingested
>>> is it particulate ? == BAD
SHARING TANK ? == BAD
TOO SHORT A PHOTOPERIOD (lights are not kept on long enough each day , will make beardie think it is winter , recommend at least 14 HRS PER DAY)
FEEDING SCHEDULE (I recommend at least 2 hrs lights/heat on before first live feed and after last feed of the day)
>>> when are you offering live feeder insects ? what are they ? how big are they ?
>>> when are you offering greens and other veg ? what are you offering ?
good guide is here :
http://www.beautifuldragons.com/Nutritionframeset.html