Answer: Check the whitish stuff carefully; if it is soft, it's a fungus and indicates the soil is too soggy or air circulation is poor. If it's hard, it's simply a salt build-up, which is common. Fertilizers and minerals in the water can build up. You can leach the salts out by drenching the pots occasionally, or by using distilled water.
You can scrape the top half inch of soil out of the pots and replace it with fresh potting soil, or you can repot all of your plants in fresh potting soil. Best wishes with your houseplants!
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