Thank you for waiting. I'll start you with a first aid measure. You're on the right track with baths, but we can make them better. Buy some unflavored Pedialyte (yes, the kind for human infants), and prepare a shallow warm bath consisting of 1/2 water and 1/2 Pedialyte. Soak your dragon for about 20 to 30 minutes. Repeat this twice a day. That will help with any dehydration.
Another way to help is to make sure the temperature in the enclosure is kept at 85 to 90 degrees day and night. The bottom of the cage should be 85*F.While it's usually recommended that the temperature be lowered at night, when they're sick, it's better to keep them warm all the time.
Normally, you’ll want daytime temperatures between 84* and 88* F and night time temperatures between 75* and 80* F . You also need to leave that mercury vapor bulb on for at least 12 hours every day. It provides UVB light as well as warmth. Water dragons need that UVB light every day or an illness called Metabolic Bone disease (MBD) develops. It causes a slow and painful death. If someone in a pet store told you otherwise, they were wrong.Without adequate UVB, calcium can't be metabolized. Your dragon may already be in the beginning stages, but with both adequate UVB and calcium, it can be reversed. If the light makes the cage too warm when it's on for 12 hours, move it up higher. Just make sure nothing blocks the rays - no plastic or screen between it and your dragon.
You may want to consider a different substrate. Bark tends to dry out quickly, and can lead to impaction and eye infections. Water dragons need humidity at 80%. It’s difficult to keep it that high. After months or years of low humidity, it can have an affect on their health. Soil holds moisture much better. Live plants in the enclosure, misting several times a day, and keeping a solid cover over part of the top can all increase humidity. If you use a cover, don’t block your UVB light with it.
I suspect that you got your information on care from pet store personnel. Unfortunately, such information is often inaccurate. While pet owners should be able to rely on pet stores, the staff there is often not well-informed. The stores are in business to sell things, not to ensure the animals’ health. Many reptiles die each year because of it. The following link has much information on care. It’s really like a whole book on water dragons. I highly recommend it as a source of information.
Water dragons are omnivores, and they also need plant foods to prevent nutritional imbalances. Many different fruits and vegetables can be used. If the dragon won’t eat them, they can be used to gutload crickets, and get them into the dragon indirectly. Here’s a link to a section on diet from the above site:http://www.triciaswaterdragon.com/diet.htm
Many times, the cause of appetite loss and weakness is simply that conditions haven't been quite right for several months. Try leaving the light on and a Pedilayte soak. If your dragon doesn't perk up in a few hours, he is most likely truly sick, and will need to be seen by a reptile vet. He may have a bacterial infection, parasites, or another issue needing treatment. This link will take you to a directory of reptile vets if you end up needing one:http://www.anapsid.org/vets/index.html#vetlist
You may want to read through the information there to see if there are other changes you’ll want to make. If you have more questions, just let me know by clicking on REPLY. I hope your dragon will be fine.
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