Nice advice, but blacksoulimage lives in Okinawa, Japan so I'm not sure if places like Walmart have extended their reach there yet (but certainly possible).
BSI, he does need a bigger tank. Any secondhand/thrift shops, places of that nature around you? Look for a used tank. Could you put a wanted ad in the base newspaper? My RES was quite a bit smaller than yours when we lived in Japan, but I used a big (as big as I could find) plastic storage container to keep him in. Do they have anything like stock tanks there? Even something like a bathtub/ofuro would do. Can you get a kiddy pool in the base store?
From what you wrote, it sounds like your turtle is shedding. As the scutes lift off, air gets under them and gives them a dull, whitish look. Have any come completely off? Is the shell hard and healthy looking underneath?
Giving him the opportunity to bask in the Okinawa sun (it's warm there all year, yes?) would do a lot for his shell. If you put him outside, though, don't leave him in the glass aquarium (will heat up too much), and he should have some shade to go when he want's to get out of the sun. Supervising him when he's outside would be good, otherwise, make whatever he's in escape proof and predator proof. (I'm envisioning some kind of outdoor enclosure/pond where he can enjoy the weather.

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"You become responsible, forever, for what you have tamed." -Antoine de Saint Exupery-