Not sure that’s true. Mine got humongous and took about half of my 180g tank( not a single one but 3 together)I got rid of a bunch as they were getting too big and stinging other sps and zoas. I had at least two that would open to the size of a volleyball but when lights go out, shrink to the size of maybe a softball. The one I have now I have to keep it in a corner by pointing flow from power head right at it