Hi Wendy,
As Mr. Limpid sez, it's all about tank size in this case. Unfortunately, they do get large (I really like them), however, they generally show up in the trade on the small side, so unless you want a tiny fish in a huge tank, you'll need to have "upgrade" plans, or if you have the tanks already running, you'll just need to move the fish as it grows. I know lots of peeps say "upgrades never happen", but we've done it ourselves with our volitans (went thru 4 tanks), and now several of our other fish have "moved up" from their grow out tanks.
BTW, I tossed some monofilament and shrink tubing into the mail on Saturday, so look for it...just a regular envelope.