montipora digitata can geta bit "weedy". However, aside from the shrooms, there is no reason to avoid things. As long as you put your GSP or xenia on a rock that is separate from touching other rocks, they won't spread. You can just remove the rock to trim the colony.
Mushrooms do tend to pop up in weird places all on their own, so unless you want mushrooms, it may be best to avoid them.
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Brad
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