pH in Aquaponics

Chinmay Rajwade, Co-founder, FARMVARY

As we promised in our previous article, here we are dropping our bit of experience and knowledge about adjusting pH in your Aquaponics system. It has always been a struggle for new growers or even commercial growers to manage pH in their Aquaponics system. Let us now understand how to get rid of pH problems permanently.


We will understand this with the help of various scenarios that generally take place in majority of cases:

  1. I have a little hard water (a little high pH), what do I do?

Let us start with basic, if your water is a little hard that means there are carbonates in the system and they are the reason why your pH is in the range of 7 or 8. Let me be very clear about it, this isn’t a bad water to start your aquaponics system, below is the list of reasons:

  • The nitrifying bacteria and the fish are generally seen happy in slightly higher pH which is good for your system as it promotes nitrification
  • The nitrification process has a by product called nitric acid, which helps to reduce the pH in your system, even though this will be very slow, it is the most natural and effective method to bring your pH

When your system has a bit of carbonates we recommend that you do not add any extra acids for the quick results. The reason being, your system will crash, want to know how?

It is pretty simple, your carbonates will react with the acidic solution that you have added and it will lead to their precipitation and hence your pH will drop drastically to such a low that the most important process of nitrification will come to a halt, that is a bad bad thing to happen!!

What to do then?

As we all know, bacteria love it when they are allowed to colonize on the biological surface area in your system (We will get into what biological surface area is later), the best way to deal with this scenario is to increase the biological surface area, add an extra grow bed, add some more material in your biofilter, just give more space for bacteria to colonize. This will boost your nitrification leading to lowering of pH. I agree to the fact that this process is a bit slow but trust me it is the most effective process. Let us now move to the second and most common scenario.

  1. Water in my system is very hard, what do I do?

Some areas do have a problem with their municipalities providing hard water, this problem is also observed when people use bore well water in their system.

A lot of people have tried getting the pH down in such water source by adding multiple acids to lower the pH, but it hasn’t fructified. The best solution to this scenario is to get a RO (reverse osmosis) filter to get rid of carbonates. An RO filter will remove literally all the carbonates in your water leaving you with pure and soft water. It is safe to use it in your system.

  1. The nitrification process has lowered my system pH to a great extent, now I want to raise it, what do I do?

This might actually happen in your system as it gets older and stronger. The nitrification process releases nitric acid which lowers the system pH, and over the time when nitrification is very strong, it will lower your pH to the rang of 5.5 to 6. Your fish or bacteria will suffer in this pH range, so what’s the solution?

The simplest solution here, is to add simple hydroxides to make your solution. Most preferably we recommend adding Calcium hydroxide or potassium hydroxide. There are two good reasons for adding these:

  1. It makes your system alkaline
  2. It helps increasing levels of calcium or potassium in your system, which is really good for the plants

As we have now understood the three scenarios let me tell you some safe methods to lower your pH artificially:

  1. Adding Acids:

Adding acids is safe as long as you are you are adding permitted acids and in little quantity. What are these acids to be used?

  • Nitric Acid (even though it occurs naturally in the system adding a little won’t harm the system)
  • Muriatic acid
  • Phosphoric Acid

We strongly recommend using phosphoric acid in the system as it adds the phosphates in the water along with reducing the pH. Also, it is very safe for both fish and plants. The phosphates have a tendency to increase the Algae in your system, so if you already have a huge algae problem please use the other two acids.

We strongly recommend not doing below things:

  1. Adding citric acid is strictly prohibited as it will kill the bacteria (Lemon, orange juice etc.)
  2. Adding vinegar
  3. Aquarium pH down solution
  4. Adding hydroponics pH down solution
  5. Adding any other acid apart from those mentioned above


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