Corn snake death

Question
QUESTION: We bought an albino corn from Petsmart and it was very active and healthy. It ate well for the first 5 times - once a week. But I tried to feed it 2 days ago and no luck - I did notice it was getting listless and less active over time. Today I found it dead in the cage with the green spot in it's belly. I'm not sure it properly digested the last pinkie I gave it about 10 days ago - never saw it come out. Any ideas - we would like to buy a corn again but I'm not sure how to keep it alive when I expected it to be easy to care for.
Thanks!
I asked Kevin but he said this was out of his expertise.

ANSWER: Sam, sorry about your loss.  Corns ARE typically super easy to care for.  The fact that yours ate at least 5 times means he was probably healthy to start with, so what happened?  Maybe it was something you did, maybe not.  It was a baby and in nature not everything survives.  Animals don't get check-ups, shots, etc.  Some live, MANY don't.  The green spot you saw was just necrosis setting in.

So, what do we do now.  You can tell me exactly how you had the cage set-up and and then I can look that over for problems.  Biggest, most common mistake made with baby snakes is improper substrate (bedding material), what were you using?

I will tell you to try and avoid Petsmart for your next snake and to instead look for a local breeder who could better answer your questions.  Local reptile shows are also a great place to look and probably the cheapest place to buy.  

---------- FOLLOW-UP ----------

QUESTION: Thanks for the reply! I think I know what happened or at least am guessing...
We use T-rex Sani-Chips for the substrate. I think I did not thaw my last feeding well enough - I never saw it come out of the snake and it was lively before that feeding - it ate it properly but seemed to slow down after that - never ate again. Also - I was using tap water and not purified or treated water - I think those are the 2 culprits - at least from my amateur snake experience!
I'm waiting a bit to buy again - I don't know of any local breeders and the one independent pet shop I know wants twice as much as Petsmart - I would not buy from Petco personally - and Petsmart does have the albino breed that I really want.
We enjoy many pet types in our family so living with nature's consequences is normal - I just try to prevent spending a lot of money and then having something die so quickly - but I know what to pay attention to next time!
Thanks again!

Answer
Tap water is absolutely fine.  I've used it for 20 years.  Santi-chips are usually pretty good as long as they are made from Aspen.  Check out www.kingsnake.com, www.faunaclassified.com, and www.lllreptile.com.  The first one is a huge site where you could find both a breeder and a local show.  The second works the same but also let's you check out the breeders reputation in the industry.  The 3rd is a well established company out of CA which I trust.  Look for a local show first, you will always find the best deals there.