Mama se Mama sa, ma Mimosa!!

I have 4 plants of different sizes now. The only thing to report this week is that the second biggest looks quite unhappy. She has some white dots, and I spotted a few gnats in the tent. I don't really know what to do except focus on keeping the space clean and provide good nutrition so they grow up strong, but it's still too early to start adding anything. It's unusual that it's only affecting one plant. In any case, I will do what I can and hope for the best. Also open to suggestions on this.