Aquaponics - pH buffering

In aquaponics, one issue that can effect your success rate is the pH of your water. pH is a measure of water's (or soil's or whatever's) level of acidity and alkalinity. A pH of 7.0 is considered neutral and also is what pure water measures.

Actually when we measure pH what we are really doing is comparing the relative quantities of two molecules. The hydrogen ion H+ gives us acidity, and the hydroxyl ion OH- gives us alkalinity.

The process of nitrification is acidifying, but in aquaponics we aim for roughly neutral water around the pH 7.0 mark. Depending on the media you use in your garden beds, your system's pH might not be close enough to 7.0 for your liking. Because the bacteria tend to make their world a little more acidic, the water will dissolve anything more alkaline than the current pH of the water. What this means is, if you have something like calcium carbonate, say in the form of shell grit* in your system, your clever system becomes self adjusting. Shell grit seems to have a pH of around 7.6. The more acidic your water gets, the more shell grit gets dissolved. This brings the system back into equilibrium. The shell grit will last for many years (depending on how much acid there is).

The shell grit is trying to get the water to pH 7.6, and the bacteria are forcing the water toward 6.0. Hopefully the result is your ph settles somewhere near 7.0 and everything gets along just fine. Plants also seem to enjoy a pH of 7.0, and that pH level also allows for the maximum availability of various trace elements to be liberated from the system and offered around to anything that wants them.

Shifting an aquaponics system toward acidity is a little harder. Most people add lemon juice, or vinegar. The test pictured to the left is the one at the top of the page but with 2 drops of lemon juice added. The problem with adding acid is that it would have to be done on a regular basis which is why we need to be careful not to use anything too alkaline as our grow bed media. Some people have gotten into trouble with limestone and marble.

Over the last few days I've been doing experiments with softwood charcoal, and have found it to steer a system toward being more acidic on an ongoing basis. The tests have only been going for a few weeks. The problem of a too alkaline system needs to be avoided from the outset, but if you have very alkaline water (say from a bore) charcoal might be a good way to pre-treat your top-up water and the initial water you use in your aquaponics system.

*shell grit is available for a few dollars a bag wherever you can buy chicken feed. Its made by crushing oyster shells or similar. Chickens eat it for the calcium they need to make egg shells.You can also use egg shells or snail shells for pH control in your system.


  1. I have been reading about aquaponics with great interest, and thinking I really need to start a system...because I love growing plants, and I've always enjoyed keeping fish, (and eating them, although up until now not the ones I was keeping), and I would LOVE an excuse to have a greenhouse, and also because, you know, I need ONE MORE THING to do in my "spare" time. And when I found a website that mentioned using worms in the grow beds, I got even more excited, because I do vermicomposting and I love my worms and how they eat all the stuff I used to throw away and make my plants look so much healthier, and the thought of putting everything I love together into one big system is just...completely irresistable. So last night, I was thinking, "but what about my chickens? Where do they fit in to this whole all-in-one gloriously harmonious circle of life?" Now you have answered that question too. Fish and plants and worms AND CHICKENS! Can it get any more perfect???

  2. Cool!

    But watch out for adding warm blooded things to a closed system. ie dont be tempted to raise chickens on a growbed, and have it self cleaning or whatever. Dont add warm blooded animal poo to an aquaponics system. Or turtles. The chickens (and other warm blooded things) can introduce some nasties. But chickens eat worms, and garden scraps, and offer eggshells, and fish eat worms, and people eat everything!

    I've had to go back to store bought eggs since we moved from the country, so I've almost stopped eating them :(

    I miss hanging out with my chickens.

    We had a zillion year old chicken called "Chicken in a box", that couldn't walk. We would take her out when we were gardening and pour her onto the ground that we had just dug up and she happily pecked around for a couple of years like that. She didn't seem to be in any pain, so we couldn't see any reason why she couldn't go on. I wanted to make her a peck controlled set of chicken wheels so she could motor around at will rather than rely on us. (inspired by some crazy guy on you tube that put a camera above his fish tank, and put wheels on the tank. The camera detected the fish's position, and the device would move in the direction the fish was looking. It could slowly move around his house at will.

    We in the west have a lot of resources.

    Make a system, you wont regret it :)

    1. I think my husband realizes it's pretty much inevitable, at this point. My dad has a fish farm back in Texas (we live in Washington State), and a greenhouse, so it's kind of in my blood.

      We're currently in the process of buying a house and getting back out of the city. The house we're buying has a 30x70 foot quonset building included. The quonset building is unassembled in large curvy pieces on the ground that look like giant fingernail clippings in Google Earth (which made me *have* to go see this particular house when we were house-hunting, just so I could find out what it was), so our first project (after moving in) will have to be assembling it.

      I'm thinking it would look real nice with a greenhouse stuck on one end of it. It's a good look for quonset buildings, don't you think? I am working on convincing my husband that all the most popular quonset buildings come with greenhouse end-caps. Fortunately, he's generally pretty agreeable.

      I had a neighbor (several moves ago) who had a duck like your chicken. Last I heard he was trying to build some sort of duck prosthetic device to let the duck move around outside his box. You would like him. His duck house (more of a duck palace, actually) had its own septic system. He told me he didn't smoke any marijuana for a whole month while he built it, so he could make sure he got it all just right. Now THAT'S commitment.

    2. There is a very definitive page that should convince your husband about the greenhouse addition here...

  3. P.S. I realize I wasn't very clear about my intentions regarding the chickens and their contribution. I wasn't planning to plant the chickens, or let them into the grow bed. There would be too many things there they would happily eat or otherwise destroy, plus they'd poop on everything. Which would make the worms happy, but not so much the fish and plants.

    Also, I don't think my chickens are very good swimmers, so the tank wouldn't be a good place for them either. It was their eggshells I had in mind, for buffering the pH of the water.

    I do, however, have a water/pump-controlled contraption in mind for operating an automatically opening/closing chicken coop door to be installed in the new digs I will be building for them once we move, and now you have me madly trying to think up a way to incorporate a solar panel into the mix, since there will be all of that water just sitting there doing nothing other than opening or closing a door every 12 hours or so. It could, obviously, charge up a battery to run the pump from, and adding a little warmth to the coop would be nice in the winter time, but not so much in the summer, and I don't think that moving the reservoir in and out seasonally would be a good solution. I prefer more of a "set it and forget it" type of solution.

    My invention machine is a little slower and less sophisticated than yours, I think, but I've got some time to ponder on it while I clean out the garage and start putting things into boxes, so maybe something will come to me.

  4. Hi!! I got nice information about pH device. It is nice article, Thanks for sharing great blog for us. pH buffering


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