In an aquaponics system the biologic reactions are constantly bringing the pH down. I developed this point in other videos and explained how to maintain the pH in the desired range. I still receive the question “How can I lower my pH” frequently so in this article and video I will respond to this point.

Why would you need to decrease your pH?

I see 2 situations where you can desire to decrease your water pH.

  1. You have limestone in your system (generally in your media).

If this is the case you made a mistake when you selected your media and didn’t follow the recommendation I give in my videos to test the media with vinegar before using it. In this case I would simply advise to change the media and replace it with an adapted one. This is a lot of work but probably the best solution.

  1. The water you are using to top up your system has a high pH.

If the water you are using is too hard, you can condition the water before using it.

The 2 ways to decrease your water pH

Reverse Osmosis method

First you can use a reverse osmosis filter. This will push the water through a membrane and will leave you with a water almost pure. Unfortunately this process consumes a lot of water and is therefore not really sustainable. Also you can’t use the water as is, you will have to re-balance the pH by adding carbonates and other minerals.

Phosphoric acid method

I would recommend to stock a large volume of water in a tank with aeration and to add little quantity of phosphoric acid until the pH reach the desired level. I don’t recommend to add the acid directly into the aquaponics system as it could drop too quickly due to the carbonate buffer being neutralized. When you manipulate phosphoric acid it is important to be well equipped with gloves and protective glasses.

A lot of different acids are available but they are not all adapted to aquaponics. The advantage of phosphoric acid is that it increases the phosphorous available for the plants.


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How to decrease your water pH in aquaponics: this is what we’re going to see together in this video. So my name is Jonathan and my aim is to help you to build and to maintain a sustainable aquaponics system in your backyard and to produce some sustainable and healthy food.


So today, I’m going to show you how we can decrease the water pH in aquaponics. I previously made a few other videos about pH in aquaponics. I explained to you that the pH is regularly decreasing in an aquaponics system, and this is due to some biological reactions that are happening in the water, in the grow-bed, thanks to bacteria.


So the pH of your aquaponics system is decreasing with time and we would need to maintain it in a certain range. So most of the time, we need to increase the pH. But today, I want to let you know how to decrease the pH. So why would we decrease the pH? Simply because sometimes the water that you’re going to use to feed your aquaponics system is going present a pH that is already high. The other reason why we would have a high pH it may be because of the media we use.


We know the media that is the grow-bed sometimes if you don’t select it properly, and I made some video about media, how to select the adapted media for your own aquaponics system.


If you haven’t watched the video, and if you already bought some media that is not adapted, you may have a high pH in your aquaponics system due to this media. If there is some limestone in the media, the water pH may increase.


Another reason and this one is will be more concerning is if you have a tank that is made out of concrete and that is constantly releasing some particles and basically increasing the pH of the water. If for any reason you added limestone in your aquaponics system, I will recommend to basically fix the issue by replacing the media or replacing the tanks not always constantly having to decrease the pH.


But if the water that you are using is already very high in pH, you may want to decrease it. If for example you have the water where the pH at 8 or above, you may want to decrease it to 7, 7.2 or 7.5 let’s say.


So to decrease the pH of the water that you’re going to use for aquaponics, there are different ways to do it. One of the very famous ways is to use a filter, an osmotic filter. So basically, we call it reverse osmosis using a filter that is going to basically push the water through a membrane. It’s going to return all the solids or all the minerals that are in the water and on these molecules of water, I’m going to be able to go through.


So when you use a reverse osmosis filter, you’re going to have one part that is going to go in the filter the pipe from your tap basically and then you’re going to have two outlets. One outlet when you got the water that you want to use another outlet where you got the water that is waste.


So yes you can always use the wasted water for your toilet or whatever but most of the time this water is completely wasted and that’s why I don’t really like those types of filters. Also they use a bit of electricity. It’s not really a positive system in terms of water consumption and energy.


The other way to do it is to basically decrease the pH, thanks to some acids. So now for this second way, please very careful. Don’t add any acid and especially not in your aquaponics system. So most of the time the acids they are linked to a particle. So you can use chloric acid or those types of things but then you have chlorine in the system. So you can use citric acid. You can use a lot of different acids, right?


But it’s not what I recommend. I recommend only to use phosphoric acids and the reason why is because phosphorous is very important for the plants. Plants need phosphorous to grow. So if you have some particular phosphorous that are added to the system, it’s not going to be an issue.


Now, when you use your acid, I don’t recommend to add it directly in the aquaponics system because in aquaponics in the water you may have some carbonates. I made some video KH. KH is basically a buffer made of carbonates and the more you add acid and the more the buffer is going to decrease but the thing is when you add acid into the system if you have a lot of carbonates, you are not going to see the pH decrease. So you’re going to think, “Okay, I’m adding 10 milliliters of acid. It doesn’t decrease. I’m going to add 50. It doesn’t decrease at all. Well, maybe it needs way more but the reality is that each time you add acid in the system the buffer of your system, the carbonates, they decrease. They decrease. They decrease. And one point, you reach the point where you don’t have buffer anymore.


And then as soon you add more acid poof! The pH drops at once. So it’s very complicated to basically regulate the pH of your water to know exactly the quantity of acid to add. So what I recommend doing is to basically regulate the pH of the water that you want to add in your system.


So basically, you’re going to use another tank and in this other tank, you’re going to add the water that you want to later add in the system. You’re going to add this water with the high pH and in this tank, you’re going to add the acid so the phosphoric acid, for instance. So you add the phosphoric acid and you look at the quantity of acid that you need to get to a pH of 7, 7.5.


So to know the quantity, you may if you want, just take a bucket of 10 liters and you do some trials with your acid, phosphoric acid. So you add a few milliliters and you see how it reacts and you see how the pH evolves. So you add your acid. You have a pH test kit and every time you add some acid in the water you get your pH test kit and you look at how much the pH evolved. And you add a bit more until you reach the pH you want. Then you calculate the number of milliliters of acid that you need to balance this quantity of water and then if you are 10 liters and you used 10 milliliters of phosphoric acid, then if you want to do 100 liters you multiply the quantity of acid by 10 to do the quantities that you want to add in your aquaponics system.


It’s very simple but I think that’s the best way to do it. I would not recommend to add the acid directly into the aquaponics system because as I explained before, you can have the pH that drops and if the pH drops, it may affect the fish and the bacteria. So now when you manipulate the acid, please be very careful because it can be dangerous. You know, you don’t want to have any contact with your skin and no splashes in your eyes. It can definitely burn your eyes. So when you manipulate the acid, just wear some safety gloves and safety protective glasses, right? This is super important.


So this is how your decrease the water pH of your aquaponics system. Now, again, I don’t think this video is going to be useful for a lot of you. Myself here, I never need to decrease the pH. I always need to increase the pH. Most of you guys it’s going to be the case so watch the other video of how to increase the pH in aquaponics but if for some reason you have some water that you need to use for aquaponics and this water is very high, use this technique of phosphoric acid or buy an osmosis filter but again, the osmosis filter is not very sustainable and as I like to say, aquaponics, the aim of aquaponics is to produce some food that is healthy, tasty, and sustainable.


When you produce some food, you want to make sure you have a very light impact on the planet. It’s better for you in the long term, better also for your kids, and better for your wallet.


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