Bearde dragon

Question
QUESTION: Why does my bearded dragon turns yellow and black head,and after a day it dies,the temp. of tank is correct enough water,it get calsium drops once a week,fresh vegatables in small pieces,ligtning in tank at day time is correct and nightlight on at night  and tank does not become warmer than 33 on hot side and 30 on cold side,get crickets every day What might be wrong?All dragogons dies in tank after say six months

ANSWER: Sounds like there's something fundamentally wrong with the enclosure. Do you have proper UVB lighting installed? Are you feeding crickets that are larger than the distance between the lizard's eyes? Are you keeping it on sand or non-natural particulates? Any of these can cause death as you've described. My best guess from what you've described would be impaction due to the wrong substrate, particularly walnut shell or calci-sand.

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QUESTION: The floor is a green mat like a pool table surface with a under mat heater which is off at this stage because it is summer and uv lights is correct globes the crickets we feed is small size?

Answer
That's strange ... there's definitely something going on. I suggest becoming a member of http://www.beardeddragon.org/ and asking some of the members there. They have definite expertise when it comes to how to keep them happy, and can probably shed more light on your issue than I am able to. Aside from that, it's a great community that would be glad to have you. Good luck!