Those little black bugs flying around your houseplants most likely aren't "fruit flies." They're probably fungus gnats, and sand and patience make a good team to get rid of them.
Effective measures against fungus gnats in the terrarium - Insektenliebe
Detecting and combating fungus gnats - Moowy UK
24Pcs Yellow Stick Fly Catcher, Yellow Boards Fungus Gnats Fight Indoor Plants Potted Plants Yellow Stick, Waterproof Yellow Trap Mosquito Trap Sticky Trap for Fruit Flies Mosquitoes Aphids Nematodes
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How to get rid of fungus gnats on plants - Los Angeles Times
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Fighting Fungus Gnats
The easy way to get rid of Fungus Gnats on indoor plants (once and for – lovethatleaf
Fungus Gnats! I'm losing this war against fungus gnats I've been fighting for months. Looking for advice. Details in comments. : r/microgrowery
4 Tips to Fight Fungus Gnats – We The Wild
How to really, truly, finally get rid of fungus gnats for good: We asked the pros, Homes
HOUSEPLANTS: HOW TO FIGHT FUNGUS GNATS
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Fighting Fungus Gnats