Yup, sounds like scale. Once you have it you've got it for ever. The way I combat scale is: look for it everytime I water, and if I have the time deal with it immediately. If not take care of it ASAP. I use Cygon. Not sure the active ingrediant but you can find that on the web. First I decide if a frond is too infested to keep; if not cut it away. Then using a fingernail or twig I scrape off ALL the remain scale even try tomove the whit crawler phase if possible. Then spray with Cygon at about 1/2 to 3/4 strength. Be advised that the pesticide may damage any new fronds. I also try to water mine first. Cygon is a systemic so I'll occasionally dilute it a little more and pour it into the root ball. Some ferns seem more prone to scale. Also scale may be building up on nearby plants. Scale doesn't like air circulation. I find little if any scale on Stags I hang in the trees during the summer. Scale especially likes Hawaiian tree ferns, birds nest, and the polypodium family. Best of luck. If you're in the Houston area you might come to a Texas Gulf Coast Fern Society meeting.

Cygon has been recalled. It should no longer be in the stores. And it shouldn't be used indoors. Though there are other systemic insecticides out there, few are labeled for indoor use, so be sure to check out your options carefully.