I find that native fish (sunnies, bluegills, rock bass) work well them as do most Central and South American Cichlids. Avoid slow moving fish such as catfish, plecos and bichirs.
I think you would be fine with any cichlid or native as well. If anything, your biggest issues may come via territorial issues between the turtles. You would probably be best off with 2 females, though a 210 should be big enough to mitigate any real problems, but you never know
I had no problems w/my razorback (in my Gallery) w/any tankmates.
Bichirs
Rays
ATF
Plants
Juruense
Tigrinus
Plecos
Discus
Baby Loaches
Stiff Bagarius Suchus
Kitumba frontosa
List goes on w/no nipping ever
From looking at different RazorBacks, I think they are aggressive towards fish due to lack of eating. I know little to none of reptiles but I assume turtles store food in their shell like camels store water in their humps. I fed my guy a variety of food daily n he had the best looking arc on his shell I have ever seen. Again it's just my thoughts so it's far from hard facts