Spot on—those are 100% spider mites (tiny spiders). The white dots underneath are their eggs.
If you are already in late veg or flowering, honestly your best move is to trash the run and restart. Spraying flowering plants will ruin your yield, create mold, and leave dead bugs stuck in the buds.
Whatever you do, do NOT use Substral Careo. It's a systemic pesticide meant for non-edible house plants, not something you are going to consume. Scrap it, bleach and sanitize your hydro system completely, and start fresh with clean genetics!