The basis on which to choose a small nutrient tank or large nutrient tank will be:
- The relative volume circulating at any given time in the whole system
- The rate at which the solution formulation must be changed
- The estimated risk that diseases can enter the system and how effectively it can be controlled
- Capital available
- Amount of water available during the year
- Space available at the site etc.
As can be seen there are numerous aspects that should be taken into consideration when selecting the size of the nutrient tank. Each of these factors usually relate to financial and practical considerations during the growth season. The advantages and disadvantages can be described as follows:
The relative volume circulating in the whole system: With small tanks the volume can deplete quickly to such an extent that the pump might run dry causing extensive damage. This happens if there is no float valve installed to prevent such a situation. Large tanks have a considerable buffer before it will run so low that it will be below the minimum required for the pumps.
The rate at which the solution formulation must be changed: Changing the solution in a small tank is easy and cost effective since the volume of water that needs to be pumped out is very small. It is costly to change the nutrient solution in a 500,000 L tank. If the solution needs to be changed once a year it might not be that expensive but usually it requires at least four to five changes a year. Dumping large amounts of water is also a problem and harmful to the environment.
The estimated risk that diseases can enter the system and how effectively it can be controlled: This poses a real problem to some growers. If a disease such as Pythium or Phytophtera enters the system and the tanks need to be cleaned, it is obvious that a small tank will be easier to clean. Comparing the price between small vs. large tank is not that straight forward. Obviously capital is one of the important factors, but system size, pump capacity, method of applying fertilizers etc. are all factors that need to be taken into consideration at the same time.
Amount of water available during the year: large tanks provide and excellent buffer if water is in short supply during some periods in the year. If a large tank is used as a reservoir, it can be used to provide some water for the plants if the pump system is down. A good estimate is to have at least two days of water in a reservoir available at any time for emergency situations.
Space available at the site: This is an important consideration. Just because there is very little space available does not mean that a system cannot be installed. Installing a small tank one should make sure that there are systems in place to warn the farmer if water runs low. It is also recommended that the nutrients should be automated when using small tanks so as to reduce the fluctuations in nutrient levels on a day to day basis. Small tanks are easy to install below soil which saves some space above ground.