What are these tiny white dots from?

Hey there DoorStop, actually what it is , is you have magnesium deficiency. You can tell it's not spidermites because they leave sharp bite marks on the leaves and when you look underneath them you find little black spots. For magnesium deficiency you can tell because of the way the yellowing happens on the serrated edges of the leafs , sometimes starting at the base. What you're using Grow Big has everything you need in it.... except cal mag. To fix this : nothing easier , just add calmag. usually the problem stops spreading very quickly and the plant fully recovers after 10 days , but if you're impatient it can recover even quicker if you use it in a spray. hope this helps ! 🚀