Overflow Tank: Save Aquaponic Nutrients

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Having an overflow tank in the event of a pump failure saves nutrient rich water from the aquaponic system.  

An overflow tank is a component which prevents the nutrient rich water in an aquaponic system from being wasted by containing it, whenever there is an emergency such as a pump or power failure. 

The overflow tank should not be confused with the sump and holds excess water in cases of emergency. The sump on the other hand, is the component which houses the pump. 

Aquaponics is the combination of aquaculture (growing fishes in tanks) and hydroponics (growing plants in nutrient rich water), where microbes convert the waste from fishes to nutrients or fertilizer, for plants to grow, in a recirculating system.

We all know that saving water is a good thing especially when it is the driving force behind this type of gardening. But what makes this water so special that we want to put things in place to prevent losing it. 

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Where does Aquaponic Nutrients Come From?

Aquaponic Nutrients come from fish waste. The fish waste contains ammonia which is converted into nitrites and then nitrates in two sequential steps by beneficial bacteria Nitrosomonas and Nitrobacter. 

This process is called nitrification

These nutrients are rich in nitrogen and plants in an aquaponic system use these nutrients to produce lush green leaves. 

Plants also require other nutrients apart from Nitrogen (N) for healthy growth and they include both micro (required in small quantities) and macro (required in large quantities) nutrients. 

Most micronutrients which the aquaponic plants require are supplied by the food which are being fed to the fishes. 

The micro nutrients includes : 

  • Magnesium (Mg)
  • Boron
  • chlorine (Cl)
  • copper (Cu)
  • iron (Fe)
  • manganese (Mn)
  • molybdenum (Mo)
  • zinc (Zn).

Plants also require other Macronutrients such as potassium (K) and phosphorus (P) to be added to the system either organically or directly. 

For example potassium (K) may be added to the system by adding over-ripened or dark to black banana peels directly into the bio filter. 

Kelp meal concentrate also does a good job. This would create a slow release of potassium into the system and would prevent shocking the plants.

Phosphorus (P) can be added to the system by using chlorine free super triple phosphate or rock phosphate in a quantity of 20 to 40 ppm or parts per million in your system for fruiting plants.

These nutrients are very important for plant growth and overall health. You would not want to have the nutrient rich water which contains all the required plant nutrients go down the drain. 

For this reason an overflow tank is important to have in an aquaponic system in the event of an emergency. 

What Size should the Overflow Tank Be?

The overflow tank should be large enough to hold the excess water from the fish tank, biofilter, mechanical filter and plant system. 

In a small aquaponic system with a 250 gallon fish tank a 55 gallon barrel drum lying horizontally would be enough to contain the excess nutrient rich water. 

Where Should you Place the Overflow Tank?

The overflow tank should be placed at the lowest point of the system next to the sump. 

The tank is usually empty when the system is running and only comes into play in the event of an emergency. 

An overflow pipe should be installed on the sump where you would like the water level to be. The pipe is then directed into the overflow tank. 

In this way whenever the water pump stops the excess water would drain straight into the overflow tank saving all the valuable nutrients. 

Can you Reuse water from the overflow tank. 

The purpose of saving the water in the overflow tank is so that it can be reused in the system. 

If you don’t have a holding tank like this, your system will have to use makeup water from the tap or some other source which doesn’t have plant nutrients in it. 

The aquaponic system would then become diluted and low in nutrients. As a result, the plants may suffer nutrient deficiencies and some may even die, until the normal nutrient levels are established again. 

The Takeaway 

The importance of an overflow tank is often overlooked until there is an emergency and the effects are seen afterwards. 

It saves aquaponic nutrients and prevents the system from shock after nutrients are lost during a pump or power failure. 

My system stuffed a power failure twice and I lost a great deal of nutrients from my aquaponic system. It’s only after seeing the effects that I decided to add an overflow tank and that problem has been totally removed. 

It’s one less thing to worry about whenever there is a power failure. 

If you would like to know how to put things in place to properly protect your aquaponic system from a power failure you can see a detailed article on how to do just that → here


JayLea has a passion for plants and has been gardening since 2015. He has valuable knowledge about gardening and houseplant care and can answer everyday practical questions that every plant owner has.

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