Answer: The white substance is probably a build-up of minerals, a rather common occurance with houseplants. You can prevent it by using distilled water, rather than tap water when watering your plants. Generally you can remove the build-up by flushing the pots and soil with copious amounts of water. Just put each plant in a basin of water and let it soak until the soil is fully saturated. Then drain and flush the soil again, until water runs out of the bottom of the pot. If you do this periodically, you'll help avoid the mineral build-up. Fungus gnats indicate that the soil is too wet. The insects feed on decaying organic debris. If you have plants that require very moist soil, you can keep the fungus gnat population down by putting decorative rock over the top of the soil. The rock will stay dry and the gnats won't be able to find a source of food.
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