Hello,
I am sorry that your baby did not make it. You had him a very short while & it sounds like he was not doing well when you first got him so I highly doubt that you did anything to cause his death. He was ill when you got him.
Is he from the same clutch then, as your other 2 are? You got them all 3 from the same breeder or store, correct?
The ESU 7% slimline desert light is not so much hazardous as it is ineffective actually. It virtually has NO UVB at all, so, if a reptile is left under that light for long durations such as several months it is highly possible that he or she will fall victim to metabolic bone disease leaving them very ill. I do not think that is the case here as he was too young to have suffered from MBD. Also, it is possible that he could have been impacted, but I cannot be positive.
The sand, especially calcisand should not be used for babies or young dragons as they tend to lick their surroundings alot & can ingest to much & that type of sand does not pass at all, or very well. It hardens up like cement & when they try & pass it alot of times, they simply cannot & they may prolapse trying to or pass away because they can't pass anything. The stool you mentioned that was all white, was just all urates or urine. If he had not eaten anything, then he would not have any waste material which would have been brown. He might have been impacted, but for such a short time, if you did not see him eat any sand, he more than likely was not. At this point, it is hard to know for sure.
He most likely was born with a viral or bacterial problem, or just a genetic problem that got the best of him, unfortunately. Sometimes, that does happen.
How are your other 2 doing?
As for the reasons why stores sell bad products, well, there are several reasons why that is. Most of the time, stores are out just for money & don't really care what type of products are sold even if they are below standard or even hazardous. There are some good quality stores, but you do have to shop around to find them.
I am very sorry for your loss.
Tracie