Thanks for the information,
Lagoon. I'll keep an eye on it to see if that's what's going on.
Ross, I only recently started spraying them because of the black spots.
I had read somewhere else that the spots might be caused by too little humidity, so I put it in a tray filled with rocks and water making sure to keep the bottom of the pot out of the water. I'll stop spraying though. Thanks for the info.