The Water Flow and the Water Valve in our FAO based system

Our friends at the Aquaponics Lab have done an interesting post last week describing the history of the Water Valve.

Lots of people were intrigued on exactly where the water valve is installed and how it’s operated. They’ve asked if we could help to clarify it by showing our FAO based system and how we operate the water valves in here using the Water Elf.

The water flow is simple, water moves by gravity as follows:

Fish Tank ->  3 Grow-beds -> Water Valve -> Sump

Finally from the sump the filtered water is pumped back to the fish tank.

Here is a quick video showing the water flow:


The water valves can be controlled mainly by two ways: A time based strategy or a water level sensor.

For real time accuracy we decided to use a level sensor and we are testing ultra-sonic one. This device uses ultra-sonic sound-waves to measure the distance between the sensor and the water surface. It enables precise adjustments of the ebb-and-flow frequency and the maximum water height inside the grow-bed while giving the ability to easily change whenever desired.

Bellow you can see pictures of the ultra-sonic sensors in our grow-bed:


Ultra-sonic sensor
Ultra-sonic sensor in place (inside the media guard)
Ultra-sonic sensors
Ultra-sonic sensor outside the media guard







Keep informed of our latest developments:







Nitrate Deficiency in Aquaponics

It has been a few months since we started the University of Sheffield aquaponics system and the plants have been developing really well:

Nitrate post 1

Although a closer look reveals something else! Last week one of our team members found out there was a kind of yellowing developing in some of our plants.

Nitrate post 2

We set out to investigate what could be causing it and how we would sort it out.

First we examined the affected plants to look for obvious pests or other diseases and there were none. So it is probably some kind of toxicity or deficiency. As the system is new and toxicities are rare in aquaponics systems we supposed it is a deficiency. The complication is that there are more than a dozen possible nutrients so we need to follow a methodical approach to find out which one(s) are deficient.

The first thing to do to identify the missing nutrient is find out if the more affected leaves are new growth / upper leaves or the old growth / lower leaves. In our case the old growth was more affected.

This means the issue is possibly a mobile nutrient (instead of an immobile nutrient); a mobile nutrient has the ability to move from the old leaves to the new ones to support the plant development therefore the old leaves show the symptoms first. Great! This eliminates almost half of the possible nutrients.

Then the next step to follow is evaluate if:

A- The yellowing is on the entire leaf.

Nitrate post 3

B- The yellowing is more pronounced but the leaf’s veins keep a green look.

Nitrate post 4

Option A is our case.

The final step is defining if the plant has necrotic stop (dead tissue) or not.

Nitrate post 5

As our leaves show no signs of dead spots the most likely nutrient missing is nitrogen / nitrate.

This is a very interesting result:

On one hand this is an expected outcome as we are feeding our system 3 grams of fish feed per metre square per day and the normal range for a media based aquaponics without solid removal is somewhere between 10 grams to 40 grams (the exact quantity will depend in plant growth/light intensity/plant type)

On the other hand the nitrate concentration is 20 ppm (parts per million) using a liquid test (API Fresh Water) and 50 ppm using a dip strip (6 in 1 Tetra test). This range is not necessarily low for aquaponics.

We will test our assumption by increasing the feeding quantities and checking the results in the following weeks.