Turtles/Box Turtle's Bad Diet...
We had rescued a box turtle from a family which had him for approximately 8 years. He was discovered when they had run him over with a lawn mower and chipped his shell. He had made a full recovery from that incident, but they unfortunately felt compelled to keep him in a 10 gallon aquarium filled with rocks and water and feed him wet dog food. He now resides in a large 50 gallon aquarium with nice bedding, a heat rock, shelter, lighting, artificial grass area and a swimming pool which loves.
However, to this day, he still eats dog food and refuses to eat anything else (though a few months ago he did take a bite of strawberry). We have tried to get him to eat commercially available box turtle food and fresh greens, fruit, and even some live foods. However, he will not.
We are aware of how finicky they are, and we have tried to wean him off of the dog food and onto a more natural diet, to no avail. So, we continue to feed him what he will eat as we try to figure out how to alter his diet. Do you have any suggestions for our situation?
First, thank you for rescuing this box turtle. It sounds like he was in a very bad situation.
My first suggestion would be to build him a pen outside. Box turtles don't do as well indoors, and they can live outdoors all year round in just about every part of the US. This winter, because you haven't had him long, I would overwinter him outdoors, but after that he may be able to hibernate outdoors. If he's outside in a planted pen with plenty of leaf litter, bark, small logs, etc., he'll be able to bask and forage for himself, and this is very healthy for him.
Second, just a few comments on your current setup. A tank isn't the best, but 50 gallon is decently large enough. You need to remove the heat rock ASAP, though. Heat rocks are extremely dangerous for reptiles and can cause serious burns. Turtles should obtain their heat from above (basking) via lighting. You didn't mention UVB lighting, but I would get a ZooMed Powersun to provide both heat and UVB (UVB is critically important for a turtle kept indoors; it allows them to properly metabolize calcium).
I'd also remove the artificial grass. You didn't say what kind of bedding you're using, but best would be about a 60/40 mix of coir and playsand (mixed together), and kept damp. Some areas should be quite moist and boggy. Box turtles need a lot of moisture, and for this turtle it's critical because he was kept for so long in such poor conditions. If he's too dry, that may be one reason he spends time soaking in his water.
You're right that he needs to get off the dog food. Even the best dog food has too many carbs for box turtles. But they can be quite stubborn, as you've found out. The best thing to do is to stop feeding him the dog food entirely. Turtles can go a long time without food because they have a slow metabolism, and as long as he keeps getting the dog food he won't change. If he gets hungry enough, and he's offered something good enough, he'll try something different.
As far as diet goes, avoid commercial foods entirely, and stick to fresh. Box turtles are fairly carnivorous, although they'll also eat greens, veggies, and fruit. Live, wiggling foods may be most tempting to him. You didn't say what you tried, but I'd get some superworms. They look like huge mealworms, but they're a different species (sometimes they're called king mealworms, but they aren't refrigerated the way mealworms are). Use long tweezers to offer them to the boxie. I have a very shy ornate boxie, and she goes wild for superworms. Make sure he's good and hungry--wait at least a few days before you offer them to him, or even a week. And don't try to feed him daily; every three days is fine until he starts eating. Other foods you can try are worms (red worms or crawlers) and snails. Those are both favorites. I don't know if you have them in your area, but Jerusalem crickets (potato bugs--those really gross-looking, big striped crickets) are a big treat.
Here's a site with more information and food suggestions for you: http://aboxturtle.com/box_turtle_diet.htm#Bugs%20and%20animal%20matter:
. Let me know how it goes, and please ask if you have more questions. Kudos to you for doing the right thing, and trying to get your turtle on a good diet!