Young plants, like just rooted clones. I'm running strong lighting in early veg, 225W COB LED, which may help explain things. Yet the substrate is really doing an excellent job of buffering. I treat it like hydroton; I pour a lot more nutrient solution in than the pot needs, by easily 50% or more, and its drainage prevents saturation. Doing this of course prevents salt buildup, another bonus.
I'm running a recirculating water system, think of it as a turbocharged SIPS. With luck, this will allow the plants to get as big as they want without being limited by pot size.