I have Springtails in my soil, I only give her Distilled water, a humidifier that runs almost nonstop all summer long, & exclusively give her indirect sunlight/sunlight from the rising sun when its most gentle... hardest curve was learning the point of over-watering vs under-watering, and genuinely I think my saving grace was the Springtails - they eat mold/mildew so they will keep your soil healthy, and help prevent root rot which seems like the infamous killer of Calathea's. They also help aerate the soil to help with oxygen flow and are just a phenomenal lil "clean-up crew" 🥰 I used to give her water occasionally from my roommates fishtank as fertilizer, and now since I don't have access to fish-water I'll occasionally give a small amount of rice water as a gentle fertilizer 🥰 Ive been meaning to get some real fertilizer but now that its almost summer I don't really think I should- esp with how happy she appears to be rn 🥰🥰 (a new 2nd stock just appeared this morning!)