nonaggressive corals that aren't ... err, are

[Peter Houde]

"Euphyllia are aggressive. Galaxia are aggressive. 'Acan' lords are aggressive." Etc. Long sweepers, yada yada. You've heard it all. Baloney. The only corals in my tank that are noxious to others are the very ones I bought as nonaggressive, i.e., some plating montis and leprechaun mushrooms. And they grow like weeds. I've got one sunset monti that is growing straight into a torch. Yesterday, some fish or snail or something broke off an arm of Anacropora. The reef glue didn't hold fast and one tiny little tip of it drooped and touched another sunset monti, which killed nearly the whole thing in less than a day. The mushrooms stunt my favia and outright kill montis they've invaded. I have to periodically prune them manually. It's a jungle out there. And there seems to be a lot of misguided advice circulating.

 

[liddojunior]

Every single thing on the reef is aggressive.
There’s peaceful corals which you might misunderstand as non aggressive. Peaceful usually means they aren’t actively trying to kill its neighbor coral with a sting.
Leathers and sponges don’t sting corals. But they release chemicals that are toxic to other corals.
And other corals are aggressive in their growth rate to take up territory. Zoas will smother out other zoas but don’t sting each other. Usually a palys will overtake a Zoa garden if neglected.
And corals also just simply grow and shade other corals. Like monti caps can just shade out entire lower parts of the tank. Or tabling acro changing flow patterns and other acro don’t get the flow they need

Aggression is usually about active stinging corals that kill neighbors outright. I don’t think anyone is saying corals don’t need pruning and careful consideration of colony growth patterns. It’s just not part of the aggression topic. It’s important to be clear that a galaxea will MURDER corals within a foot. And that’s not a foot from where the frag is starting it’s a foot from where you want the colony max size to be when it’s grown out

 

[Peter Houde]

I put some of the supposed aggressive corals in there at least in part to keep the weedy ones in check. So far, no go. That includes galaxia. It's still pretty small, but it's less than an inch from encroaching mushrooms and hasn't deterred them at all.