If it is the same head/colony, I let them grow together. If it is competing corals, I frag them. One will encrust the other. I have a Pavona decussata overgrowing an A. Microphthalma, and so on. You would be surprised how small a frag can start out as. I glued 1/4 tips of A.Nana to snail shells and they are now covered and starting to branch out. Real funny how fast these buggers grow. And before someone gets upset, the shells are empty unless a hermit finds them and moves in.
I do not let my differing spp. of sps corals overgrow one another. The one exception to this was when I noticed a porities and a purple spp. of acropora overgrowing each other. Neither one was killing the other coral off so for the time being I let them go at it. I had to move the purple acropora down as it had grown to the surface and when it came time to do so they just popped apart. There is still some of the acropora on the porities that broke off. Will wait to see if it starts growing. HTH..
