Having an aquaponics system is fun and very rewarding. Not only for the fresh and naturally grown veggies but also for the knowledge you will acquire along the way. In this article I will introduce you to a very important parameter: the pH. You may have heard about this term, mostly concerning your drinking water. Well, our favourite pets (our fish) as well as our plants like their water to a certain pH and this is for that reason, you will have to test it. So without any overdue, let's talk about potential of hydrogen aka pH.
How does pH works?
Here in Dubai the tap water is considered ''hard'' meaning the Alkalinity is high... What does that really mean? In chemistry lingo, pH is a numeric scale used to specify the acidity or basicity of an aqueous solution, water in our case. This scale is measured in units of moles per liter, of hydrogen ions. Where 4 is acidic and 9 is basic, neutral being a pH of 7 units of moles per liter of hydrogen ions... Let's look at this diagram and let our brain rest from this chemistry lesson:
What should it be?
In aquaponics, the majority of beginners want their pH water to be low because they hear about plants wanting a pH of 6 to 6.5. Many rush to the store and buy some acid, add couple spoons full to their fish tank...and BAM! first kill... If aquaponics will teach you something it's patience. From the moment you switch the pump on and your system starts its cycling process, until you see your fish hatching in the tank, all this is made by the divine Light to teach you patience. Om̐ must come to mind :)
So, before rushing head down, let's take a step back and try to understand what is the process of controlling pH.
As we see on the scale above, the neutral point is 7; so why can't we simply go neutral and stick to a pH of 7? If that was this easy... As I mentioned in the introduction, our tap water here in Dubai is around 8.5 to 9 on the pH scale, which means it is very basic. Maybe you have noticed this lately in the health websites, social pages or other Insta accounts where it's mentioned we should drink more Alkaline water to help counter the acidity we ingest (if and when) eating junk food. What is happening in our fish tank is very similar. When the system is cycled the bacteria colony by doing its nitrogen thing, is creating a slight acidic environment that eventually affects the water chemistry. So with time, what happens is that the nitrification helps our pH value to drop. This the ''patience Padawan' rule #1 part of aquaponics.
Other aspects of what is pH is linked to the ions oh hydrogen in the water and they are affected by the acid or base compounds. The higher the pH the most likely is that you have a ''hard'' water or rich in carbonates. On the other spectrum, a very low pH indicates a high level of acidity. For example, hydrochloric acid has a pH of 0 and alkali, sodium hydroxide for example, has a pH of 14.
Should I lower my pH?
If you are planning to rush to (let me know where by the way...) buy some muriatic acid, be aware, this is a very strong acid and personal protective equipment must be worn at all times!
On the other hand, I would recommend you wait and observe first hand how the nitrification is actually bringing the system's pH down, slowly but surely.
In our gentle climatic environment, evapotranspiration and plain evaporation will mean that you have to top up your fish tank or system water at least once a week. In this case and only in this case, I would recomment a top-up tank in which you would adjust the pH (with an acid) before sending it in the system where the pH is already lowered thanks to the nitrification. Here it is recommended to use either muriatic acid or phosphoric, which is safer to handle.
In this case, a type of titration method must be adopted. Let me explain what I mean by that. You are already familiar with the API freshwater test kit where you put 3 drops of pH regent to get to know your pH value. What you are doing actually is exactly how you would dose the acid in your top-up tank to reach the pH in your system water.
Here are the instructions:
1. I take 2 gallon of water from the system in a plastic bucket.
2. I use an eyedropper to drip acid in the water in the bucket testing the water after each drop until it reaches my pH set point say, 7.5. (7.5 is NOT a recommendation, just an example to show you how this works) Usually that is between 3 and 6 drops depending on how strong the acid is and the original pH of the water. Again, ours is very alkaline.
3. Each drop of acid has an approximate volume of 0.05 milliliters. So for this example, 6 drops would have a volume of 0.30 milliliters.
4. So if it takes 6 drops of acid (0.30 ml) to bring 2 gallons of water down to pH 7.5 then it takes 0.15 ml to bring 1 gallon of water down to pH 7.5.
5. I then multiply 0.15 ml x the amount of water in my system in gallons to get the amount of acid I need. So say I have 1,000 gallons of water, so it would be 1,000 x 0.15 ml = 150 ml or just over 5 oz.
Thanks for the instructions to: George B. Brooks, Jr. Ph.D. NxTHorizon.com
Another solution would be RO filter
If your water is harder, or if you simply don’t want to wait, the best thing to do is install an RO filter (Reverse Osmosis). RO filters remove almost everything from the water (including carbonates) leaving you with very pure, carbonate-free water.You can allow nitrification to drive pH down, or you can add hydroxides to raise pH (and supplement nutrients) with no long term pH effects.
RO filters can cost a few hundred dollars, but in my experience, many of the aquaponics enthusiasts who spend months struggling with pH, and artificially trying to lower it, reached the point where looking back, they wish they’d just installed an RO filter and avoided the cost and heartache of fighting the fundamental chemistry of their system. Remember, cheap is, in the long run, never that cheap.
That's it for now, I hope this was as helpful as it was fun writing and doing the research. Leave a comment below, ask questions, rates if you like and share it among your friends. Thanks :)
I am a French expat, married, dad of one, nature lover and firm believer of sustainable living. My background is leisure and tourism industry. I fell into aquaponics and now I am sharing with you my adventure.