To push the pest resistance test even further (so far, the plants have shown resilience against fungus gnats, thrips, and excessive humidity), it’s getting too risky to allow the gnats to continue affecting my roots. As a test, I sieved fine sand from my garden and spread it over the soil to eliminate the gnats' living space. I gave the plants a good watering before applying the sand, and now I’ll leave it like this for a week. By the end of the week, I plan to repot them anyway, so we’ll see if this method clears up the gnat problem.