Answer: Based on your description it sounds like it may be a mineral buildup, possibly from fertilizing. The simple solution is to scrape it off the surface. You might also leach the soil every few months by watering copiously several times in quick succession to rinse out excess minerals.
If you do not think it is minerals, and if it looks more like a fungus, again just scrape it off. A fungus can occasionally grow on material in the potting soil and will stop once the food source is used up. It will not usually spread as long as you promptly remove the "fruiting bodies" that appear and thus any spores it might develop. As long as the plant seems healthy it is usually not something to really worry about.
I apologize for the delay in answering your question!
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