Testing Water Quality

Questions and Answers about Water in Aquaponics 

What is Nitrification?
The process whereby Ammonia in wastewater is oxidized to Nitrite and then to Nitrate by bacterial or chemical reactions. Basically there are Ammonia-oxidizing bacteria (AOB) that convert Ammonia into Nitrite in the presence of oxygen for energy. Nitrosomonas is an AOB. Then Nitrite-oxidizing bacteria (NOB) convert Nitrite to Nitrate in the presence of oxygen for engergy. The most common mentioned NOB is Nitrobacter however some modern studies suggest that Nitrospira is perhaps a more important NOB.

Is Nitrification important?
Yes, it is very important because Ammonia and Nitrite are very toxic to fish. Nitrate is not as toxic to fish and the plants can use it to produce protien and nucleic acids.

Do I have to buy Bacteria to add to my system?
Generally no. So long as you do not overstock with fish and keep monitoring your system for pH, Ammonia, Nitrite and Nitrate.

How do I know if Nitrification is happening in my new system?
You should get a test kit that does pH, Ammonia, Nitrite and Nitrate. What you should see, after you put the fish into the system, is an increase in Ammonia. The Ammonia should keep increasing. Over this time Ammonia-oxidizing-bacteria (AOB) will commence to multiply. They are typically slow to multiply. Once there are enough AOB the Ammonia should decrease. This should start within one and half to two weeks. Nitrite should now start to increase in the system as AOB convert the Ammonia. As the Nitrite levels increase the Nitrite-oxidizing-bacteria (NOB) will begin to multiply in the system and the Nitrate level will start to increase. NOB are equally slow growing bacteria and it will typically take a week and half to two weeks before the Nitrite level will peak and then start to decrease. By now, if everything is going well, the Ammonia should be very low and remain like that. Nitrite levels should continue to drop over the next few weeks until it remains at a low level. Nitrate levels will vary depending on the balance of fish and plants in the system.
pH should decrease over the period as the nitrification process will make the water more acidic. Keep a track of this. pH must be above 7 for the nitrification process to work properly.

What is pH?
pH is a measure of the degree of the acidity or the alkalinity of a solution as measured on a scale (the 'pH scale') of 0 to 14. Technically it is a measure of the activity of the hydrogen ion (H+).
The midpoint of 7.0 on the pH scale represents neutrality. pH 7.0 is called a 'neutral' solution and is neither acid or alkaline. Numbers below 7.0 are known as acid. Numbers greater than 7.0 are known as alkaline.

What is a normal pH for an aquaponics system?
There is no 'normal' pH in an Aquaponic system as such. The pH level will change over time depending on the system and how it is running. The system will not settle on a particular pH and stay there. This is why it is a good idea to test the pH at least once a week.

What is the correct pH range?
The pH in an aquaponic system should be maintained between 6.8 and 7.2.

My pH is too high what do I do (pH greater than 7.2)?
This is usually ok and you do not have to do anything to 'fix' it. The nitrification process will cause the system to become more acidic over time. We have had systems with pH levels just over 8 when they started and they all went down over time.

My pH is too low what do I do (pH less than 6.8)?
It is normal for the system to get more acidic. The problem is that below 7.0 the nitrification process will start to slow.  The slowing is dramatic by the low 6's. It is important that you do not let this happen! You can increase the pH of the system (make it more Alkaline) by adding Calcium Hydroxide [ Ca(OH)2 ] "Hydrated Lime" or Potassium Hydroxide [ KOH ] "Caustic Potash". In both cases be very careful. Add a small amount of the powder to a bucket of water. Then pour it into your system slowly over a prolonged period (like a day). Remember it is very Alkaline so do not just dump it all quickly into the system.
Note: Calcium Hydroxide is reasonably safe however Potassium Hydroxide is not. Both however should be handled with care.

Photos are of aquaponic systems built and/or maintained by Martin and Kerri