Oh yeah. That was great!
I know that I am prejudiced because you bought the fish from me, but what I told you would happen is happening. The Half Blacks are fixing to spawn and are claiming their part of your tank. I love it.
I expect that they will spawn on the magnet. If you use the magnet often I suggest that next time you stick a piece on 1" PVC in their favorite corner so they can spawn on it in the future.
I love this thread. I think that I love it even more that your Discus thread. I can't wait for more.