Well, in the turtle tank they are essentially being tortured, and will eventually zig when they should zag, or simply tire out, and then they will be caught and eaten. If he doesn't catch them soon, they will learn the tank and get better at evasion; the turtle will probably lose interest in such aggressive chasing, but he won't become their buddy; he'll just slow down and bide his time.
At this point, I don't think you have anything to lose by trying them in the other tank...by which I mean that although they have everything to lose, you should come out okay.
Now, I don't mean to dog-pile on you when you are already having problems, but...does that turtle have anywhere to dry off and bask? The pic seems to show a platform that is completely submerged just below the surface; it looks like a piece of slippery glass that would be very difficult for the animal to climb onto, and needs some kind of ramp or steps to assist in this; also needs the water level dropped enough for the platform to be completely dry. You've obviously put some effort into cutting and building that shelf, might as well make it work as it should with a few mods. The turtle's shell seems to show signs of some kind of erosion or rot as well...apologies if not true, hard to be sure with that pic...and the most common cause for this type of shell problem is inability to dry off.
Sorry for the derail, and good luck with the fish.