Hi Dave no the koi have not given me any problems with the Turtles. The only thing i have noticed is the tails of the shubunkins have been nipped but they have now grown back i hvae been told that it could be the turtles or even the koi that could have done it because they have been known to in the past but they have been together for nearly 3 months and they eat together sometimes the fish steal the food out of the turtles mouths as they catch it then the turtles turn to chase them but never can so they give up and go after more food.
I have put a 200mm piece of plastic pipe in there i have attached it to a rock to stop it from floating up and cut a small hole in it so that the fish have an escape route if needed it was for the fish to go in but the little turtles use it more than the fish do. (pic1)
This pond is awesome! I'm looking At building a indoor pond for my RES turtles and this helps a lot! What kind of filter are you using? Also how did you do your corners for the linear? Are heard the corners are hard to do.