Snappy's carapace is about 13" long by 11" wide, probably around 10 pounds.
We go through a large can (20 oz?) of Repto-min sticks or Wardley (I think) reptile sticks a month plus 40-50 feeders. He gets earthworms when it rains hard enough to flood them out. I realize the feeders aren't that great, but one of the moms at our school likes to buy them for him. I also feed him pieces of frozen fish (thawed). For a while he ate frozen sea scallops, I had a bag that got freezer-burned a little, so I fed them to Snappy
I like to keep his tank fairly open, sometimes he will swim back and forth from end to end. There is about 2" of large (1"-1 1/2") round rock and assorted chunks of slate as a substrate. It does make the tank a little dirtier, but he likes to dig in it, especially in the fall.
Snappy has only been in the 300 for a couple years. Before that he was in a 75. Before that he was in half of a 75 (divided from another turtle). Before I got him he was in a fish bowl. The lady asked if I wanted him - "He's getting so big all he can do is turn around in circles" - needless to say, I took him