A submersible
pump from 70 Gallon Per Hour for the smallest garden to 200 GPH or over for
commercial size sits in your
nutrient tank and when the timer turns the pump on it pumps the solution up to the plants to the correct height which is determined by the height of the overflow pipe..
You can use a large pump for a small garden by using a flow control valve to slow the water to the
garden. Or just crimp the hose like I do sometimes.
Ron