The Auto Top-Up system is a novelty that has saved many plants for growers. It passively replenishes the water in the tank for systems using NFT (passive = without the use of a pump and electricity). You can go on vacation or the weekend and there is no risk that the plants will not have the necessary nutrients. For connecting 3 GroTanks - all necessary connectors are included in the accessories. Auto Top Up tank volume: 81 l.