LOL. My pair has spawned a couple of times. The pH was 7 and the temp was between 78-80. I would do 25% water changes once a week. The rock should be big enough but these fish can lay a lot of eggs. You might want to put a few different smooth rocks in and spaced out for them to choose from. I have never done anything special with the rocks that I put in the tank other than wash and scrub them them well. If they didn't come from a water source, it is unlikely they will carry a disease that could be passed on to your fish. I fed them red wrigglers and lots of frozen food like blood worms, brine shrimp, mysis shrimp and supplemented with flakes/pellets.
When they have paired up they will flare their gills and fins and swim in circles with each other. The colors will deepen on both fish. The pic in my avatar is my pair of FM courting. They will then choose a rock (mine always chose one that had some kind of overhead protection like a piece of wood or something) and they will clean the rock, shimmy over it and any gravel around it will be carried away. They shouldn't be far from laying eggs at this point. Good Luck!