They aren't gnats, they're root aphids. They grow wings and fly when they are overcrowded. They make it look like a nute deficiency, most notably calmag and nitrogen from my experience, and stunted growth. A sign of them is when the tip curls up and back on its self looking like you rolled it which also looks kind of like nuts burn, or a potasium def. except its not to the side. Google pics of them. They're worse than spider mites.
Not saying the plant in this thread has them, probably just hungry. But keep an eye out for them. 6 legs and looks like a tick