22 May 2019
What Is the Difference Between NH3 (Ammonia) and NH4 (Ammonium) and What Should Shrimp Farmers Care About?
Written by Zach Stein

There are many things that can kill shrimp in a pond and unfortunately for farmers, ammonia poisoning is one of them.

Ammonia is excreted in shrimp waste and normally goes through the nitrification process, converted by bacteria into nitrates and then into nitrates where it can feed plankton and algaes.

But if ammonia builds too high, it can severely stress shrimp, leaving them more susceptible to disease and kill them. Thus it is critical that farmers measure their ammonia levels to ensure the health of their animals.

But measuring ammonia is not straight forward and today requires some calculation and estimating. In this post we explore the two different types of ammonia that you can measure and their implications on a shrimp farm

NH3 – Ammonia

NH3 is the toxic form of ammonia to shrimp. It is only present when pH is higher, in the safe ranges for shrimp (above 7.5), and exists actually as a gas suspended in between the water molecules.

NH3 is also referred to as un-ionized ammonia (compared to its ionized cousin, NH4). In aquaculture, even low levels of un-ionized ammonia can be dangerous for aquatic animals. Concentrations as low as 0.05 mg/L can lead to poor growth and FCR’s and higher susceptibility to disease. When ammonia climbs higher it can lead directly to tissue damage on the animal and death.

NH4 – Ammonium (or Total Ammonia)

NH4, also known as ammonium, also known as ionized ammonium, is the form that is directly excreted by animals. It by itself is not toxic, but it contains NH3 which in high levels, as seen above, can be directly dangerous to shrimp.

Which Should Shrimp Farmers Measure?

The problem for shrimp farmers is that the vast majority of drop tests and probes test for NH4 as it is far more stable and easier to measure. Then an analyst has to use a conversion table based upon the pH of the water to backwards calculate the amount of NH3 present in the water in order to get useful data to take action upon.

Therefore, farmers are measuring NH4 in order to figure out their NH3 measurement. This presents a problem to farmers because the processes for measuring both NH4 and pH are inconsistent, especially when done with a visual, color-based drop test. Not only are these drops not cheap, but they are not very reliable. Differences in the light of the room, the control of the employee using the drops, their attention to detail, and their level of color-blindedness can lead to errors in comparing the color of the vial to the color on the sheet of paper.

This process has a high enough error rate when measuring just one parameter, but when stacking two parameters together, such as ammonium and pH, the chances for making a mistake are even higher.

We are working to solve that with Osmobot as it is the world’s first continuous monitor for aquaculture that directly measures NH3, not NH4, and uses computer vision to eliminate the errors caused by manual testing.


Measuring and monitoring ammonia is critical in shrimp farms, but the current primary methods leave a lot to be desired. Luckily help with automated ammonia monitoring are on the horizon. Stay tuned!