Hey there, I know it's scary the algae thing lol happened to me too and I panicked and removed the plant from the grow room, turns out algae is not so bad it's even a good sign and can lead to symbiotic relationship with the soil by producing nutrients like N . Basically it comes from vitathrive I think seems like the rooting agent is a kelp extract so that might be where it comes from. To kill off the growth use a different chelation agent like enzymes, beneficial bacteria or humic acid, or even 0.3% H2O2 if you're brave. Hope this helps ! 🚀