Thank you for getting back to me. Lettuce isn't a complete diet, and the tortoise will get sick if that's all he eats. The vitamin A supplementation isn't a good idea. Too much vitamin A easily leads to eye problems in tortoises. These tortoises need a high fiber diet. Hay and grasses should be a big part of the diet. Greens such as dandelion, collards, and turnip greens are also good. You should supplement calcium with calcium carbonate powder. I recommend that you read about an appropriate diet at the following site:
The first thing I would try with the tortoise is some good quality grass hay.
The tortoise may not have much of an appetite because a few things in his habitat are not optimal. A tank isn’t the best environment for tortoises to live in because the air can’t circulate properly. They should have some kind of an open enclosure that is at least 4 feet long and 2 ft. wide, and 1 to 2 ft. deep. You could build such an enclosure or convert a preformed garden pond or child’s plastic wading pool (one of the larger sizes).
Your temperatures are a bit too cool. The gradient in the enclosure should be 75*F to 85*F, with the basking area warmer yet, at 95*F. Night temperatures can go down to 70* to 75*F. A UV basking light most likely only puts out UVA rays. To stay healthy indoors, the tortoise also needs a UVB light. A Reptisun 10.0 is a good brand. Full-spectrum is not the same thing. The UVB light doesn't provide heat, but without it, the tortoise will develop Metabolic Bone Disease. MBD causes a slow, painful death. UVB bulbs are ineffective after 6 months, even though they may look fine.
I suggest that you read the information at the above site I gave a link to, increase the temperature in the enclosure, and try some of the recommended foods right away. A UVB light should also be a priority. After that's all taken care of, you can look at your options for a different type of enclosure. If you have more questions about this, just let me know by clicking on REPLY. I hope your tortoise will soon be willing to eat a healthy diet.