I thought you was talking about excessive macro algae growth. I got some grape calurpia that grows like a weed in my 20 gal
. If i let it the grape woudl choke out other desirables.
Its very possible to have corals get to big. Since in the wild they are often subject to violent storms that break the corals apart as a natural fragging process or they will split and divide.
Depending on the coral the fragging technique is different. if its a SPS
coral often all you have to do is break off a branch or have a pair of plyers and sip off a hunk to frag
it. If its a softy coral then you could simply take some snips and clip off a few parts.