Aquaponic Chemistry | Managing Hydroponic Nutrients

It is possible to monitor and control water characteristics automatically, but to do so can become complex and costly. For a commercial operation it may be very worthwhile. For a small scale amateur aquaponic system, it may be more viable to just avoid the more difficult species of plants and animals. One key thing is critical though – any changes that occur should occur gradually (eg. sudden changes in pH can cause shock and kill fish, but the same change made gradually, may be tolerated.)

As fish and plants are constantly taking chemicals from the water to use, they are also leaving other components or unused chemicals behind. The concentration of what is removed is decreasing, and at the same time, the concentration of what is left behind is increasing.

Recapping on previous chapters - there are three things that are of particular concern i.e. residual components will over time:

  1. Change the pH (acidity).
  2. Increase the concentration of unwanted salts
  3. Cause a build-up of ammonia.

As discussed earlier ammonia can be converted to less toxic nitrite by bacteria, but this is a process that can take time (about 6 weeks in fresh water). Some types of growing media will encourage the growth of these “ammonia converting” bacteria (e.g. scoria or expanded clay are both excellent for promoting this good bacteria).  

If ammonia levels do increase too much, it is possible to lower them quickly by using zeolites (a type of rock dust). If you place zeolites in water for no more than 12 hours, the zeolites will extract ammonia; but if left longer than 12 hours, the ammonia can start to leach back into the water (hence remove after 11 or 12 hours).
 

Measuring pH and EC


The pH can be measured with a pH meter – they are not too expensive and a tool that is mandatory for successful aquaponics.

The total salts concentration can be determined by measuring electrical conductivity (EC) of the water in your aquaponic tanks).

Electro conductivity needs to be monitored closely as the nutrient concentration will be continually dropping due to nutrients being taken out and used by the plants growing in the system.

EC Meters and EC Controllers


An EC meter (Electrical Conductivity meter) is a device which measures the flow of electricity between to electrodes. If the concentration of salts in the solution is stronger, there will be a stronger flow of electrons. An EC meter won’t tell you the type of nutrients in your water just the total EC.

There is much and varied information and advice on the use or effectiveness of EC meters in aquaponics however they can be a useful tool for measuring total EC.

An EC meter (Electrical Conductivity meter) is a device which measures the flow of electricity between to electrodes. If the concentration of salts in the solution is stronger, there will be a stronger flow of electrons.

A salinity controller monitors and shows the EC level in the solution at all times, and operates injection pumps which add concentrated nutrient solution to the solution in the system when the level falls.

EC will increase if temperature increases. Because of this, it is necessary to provide temperature compensation in the salinity control system. This is usually calculated on the basis of 2% per degree centigrade.

EC will increase if temperature increases. Because of this, it is necessary to provide temperature compensation in the salinity control system. This is usually calculated on the basis of 2% per degree centigrade.

A salinity controller automatically compensates for EC drop bringing it back to a predetermined level, thus maintaining optimum nutrient levels at all times.

Over a period of time, there can be a build-up of unused salts (i.e. nutrients which are not used). This can create an inappropriate EC reading which will make adjustments to the setting on your salinity controller necessary. Alternatively the solution needs to be replaced with a fresh solution.

Although salinity controllers can maintain nutrient solutions for periods at optimum levels, it is advisable chemical analysis of the nutrient solution (for nitrogen, potassium, calcium, magnesium, phosphorus and iron) also be carried out from time to time. In large commercial operations, such a chemical analysis should be undertaken every two weeks.

pH Controller


A pH controller is a device linked to an electrode in the catchment tank. The electrode measures the pH of the nutrient solution and relays the reading to the controller. The controller can be programmed to inject predetermined amounts of acidic or alkaline solution into the catchment tank if the pH reaches an upper or lower limit. This way, the pH of the solution can be brought back to a level which is suitable for the plants being grown. White vinegar is often used to reduce pH in aquaponics, and bicarbonate of soda to increase pH.

If the pH drops below 6.0, there are likely to be serious problems with many types of fish; and below 5.0 can cause corrosion in parts in the pump.

In pure hydroponics (no fish) nitric or phosphoric acid are used to correct high pH in nutrient solutions; but in an aquaponic system you must also consider how any additives might affect any fish you are growing. They are pre mixed in 1:10 or 1:20 with water and injected into the catchment tank as required, allowing maximum mixing to occur before the adjusted solution is delivered to the plants.

When mixing concentrated acids: always add the acid to the water. It can be very dangerous adding the water to the acid.


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