adding dbt to my collection?

I have a 1400 gal aquarium with around 200 fish of 25 species. Also hin the tank are 4 map turtles and 1 male western painted turtle. The turles do not bother the fish except for eating a dead or dying one.I feed the turtles floating trout pellets, sinking shrimp pellets, earth worms, and freezed dried gammarus. They also eat the flake food the fish get. I did have ared eared slider that did kill fish and would swim around all day with her mouth open trying catch the fish.All the turtles were added as babiesand are 2 to 3 years old.I would like to add some dbt to the collection and wondered if anyone had any advice?