Does it have a basking area? I would increase the heat bulb
to about a 60 watt and then check the temp on the basking area.
In case this is not familiar to you, a basking area is the
place where the turtle can get completely out of the water
and warm up. The heat light should be positioned above this
area far enough away to make it 85 degrees. I would also
purchase a larger enclosure. Huge rubbermaid containers are
great for turtles. In your 20 gallon, an increase in your heat
light will most likely warm the water also to the desired temp.
Make sure you check all temps involved, don't guess. Temps that
are too hot are just as bad as temps that are too cold. Also,
I do not recall you saying you had a UVB source?? This is
very critical to the well being of your turtle. Please do all
the research you can on your new pet. DO NOT count on employees
in the petshops. A lot of the time they give wrong information.
Oh, almost forgot, position your heat light over one side of
the enclosure that way the turtle can move from cooler to warmer
which is very important. For feeding, try Reptomin Floating
Food Sticks. If that does not work after adjusting temps, try
chicken flavored canned dog food just to start it eating. Once it begins eating it will start taking other foods.
Hope this helps and post again if you have more questions.
Linda