Alright well right now the florashield is likely your best bet, or some kind of root treatment whether its foliar or just added into the nutrient solution. you will also need to upgrade the pump, such as buying a connector to make both valves on pump going to single bucket, or some way to increase oxygen which is what you lack currently. i had a great nutrient solution like yours, but without oxygen its as good as nothing. thats why aeroponics are so effective in building root systems, 100% oxygen environment nutrient uptake!