my juvenile chinese water dragon

Question
hi donna, i recently bought my first CWD from petsmart and it is something new to me ive done research my relative has one and has had it for a while it is very healthy and he takes great care of it, so he gave me tips on how to care for it also, but i fear he is unhealthy only because i know that when lizards in general arent bright green and are turning brownish may seem to be unhealthy. the first two days were great he was very active anf running around the tank all day theres a giant artificial rock that i put water in so it can soak itself and do its business,i have the coconut powder and actually regret getting that i wish i would have bought the bark chips because everytime it gets out of the water it gets filled with the powder that sticks to him cuz hes wet hes hasnt ate since yesterday morning i tried feeding him today he never ste it till finally only ate one cricket but so far thats it i give him great humidity and heat all day and water to bathe in, but i noticed this morning he wasnt green like when i got him he is starting to get brown all on his back i freaked out and called the petstore the person said it may be that his body temperature is low but he always gets heat and they suggested i soaked him in warm water to raise his temp, i did just that and twice actually.hes still active but not as much he woke up later than me this morning when yesterday he oke up earlier i feel like hes sick cuz he does just lay around at times and not do anything just sleep but when i first got him he wouldnt do that hed be perfect. idk what im doing wrong i need help maybe hes just not hungry but i dont know i need to know how to nurture him i wont let him get worse. is there any advice you can give that i can do on my own to try and fix this idk what else to do. i guess i didnt do enough research. thanks, andre.

Answer
Ok, let's do some trouble-shooting.

Do you have a UVB light?  If so, what kind, and how far away is it from the dragon's basking area?

What are the exact temperatures on the cool side, and the basking spot?

Has he been handled?

What are you offering him for food?  (Details--size, supplements, etc).

What cage decor do you have?  (Hides, branches, greenery, etc).

I would never recommend that a first-time reptile owner buy a reptile from Petsmart.  The animals have been subjected to a great deal of stress, have been housed with others, and may have picked up who knows what along the way.  It's far from impossible that he had already been exposed to something before you bought him, and is just now showing symptoms, but before we jump to conclusions, let's iron out all of the husbandry possibilities.

Being placed in a brand new home is very stressful for reptiles, and it can trigger latent illnesses as a result, as it compromises their immune system.  A reptile may take one or two weeks to adjust to a new home.  High activity at first is normal, but the animals should settle down to some degree after that.  The failure to eat is a real point of concern, however, and indicates that something is wrong.  Let's see if we can find out what, or if you will need to either return him, or take him to a vet.