Yep. The rocks may be attractive, but they are the wrong sort to have around koi. If you are going to keep rocks in an aquarium with small koi, use smooth river rock. (Many will recommend no rock whatsoever. In a pond, I agree. In an all glass aquarium, I think a rock or two can help the koi feel more comfortable if large enough to be able to hide a bit. Be careful that debris does not build up under the rock.)
If the water is top quality, the fins will heal without a problem. Good aeration and water temps in the low 70sF make for a healthy fish. If there is excess food or mulm, bacterial populations will be high and water quality lower than desired...infection may set in.
Enjoy your little one. Soon it will be time for a pond.
