Turtle not eating

Question
Hello,
I have 8 year old red ear slider turtle. She is in a 25 gallon aquarium has a basking light, basking area and a water heater. She normally eats pallets once a day. For the past week and a half she has not been wanting to eat. I let her loose in my back yard and has been digging her self underground. I know that turtles have a time of hibernation. I'm wondering if that is the reason for her not wanting to eat. I have taken her out and attempted to feed her however she still does not want to eat anything. After attempting to feed her I let her go back to her underground spot. Help. What can I do? Should I be worried?

Answer
Well, the first thing that concerns me is that you have an 8 year old RES, that you have identified as a female, in a 25 gallon tank.  This is a pitifully small enclosure for such a large turtle.  (If she is not large, she certainly should be, at age 8).

Proper size for a glass tank should be 10 gallons per inch of shell length, minimum, so for an 8 year old female turtle, it would have to be at least a 100 gallon tank.  A plastic stock tub, or a waterland tub, of similar size, would be even better (and far easier to clean).  

You did not mention a UVB light.  If you do not have one, this is a major concern.  Sliders absolutely require UVB light when kept indoors in captivity.  UVB fluorescent lights must be replaced every 6 months.  The new mercury-vapor reptile lights which provide both heat and UVB are ideal for large turtles, and last for 3 years.  (The UVB coating deteriorates over time on these lights, which is why they need to be replaced, even though they still produce light).

Indoors, with a consistent light cycle and consistent heat, it's unlikely that red-eared slider would try to hibernate.  Before assuming that this is the case, you should definitely take her to an experienced reptile veterinarian for a checkup, and also evaluate your husbandry.  Failure to eat can be caused by any number of health problems, such as infections, internal parasites, nutritional deficiencies (lack of UVB light or any fresh foods), etc.  Such a small tank must need to be cleaned almost daily, with such a large turtle in it, so if it is not, dirty water can be a major health risk.