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Lower and Raise pH in Aquaponics System

pH is critical in aquaponics. Fish and plants both need the same range of pH. Here are some notes on Lowering pH in your aquaponics system.

Adjust pH SLOWLY!

The most important thing when adjusting pH is to do it slowly. If you lower pH too much too fast, it could stress your fish or plants and kill them. pH should be lowered over a week or more, not sooner. Murray from http://www.aquaponics.net.au says that testing pH is one of the most important things you can test and stay on top of.

pH Fluctuations

pH will vary according to what is added (rain, fish, plants). Temperature will also cause your pH to vary. If you are testing for pH, you should measure at several points in the day for an average, or measure at the same time and temperature each day so you have consistent readings.
At the beginning, when you have water without a bacteria colony, pH will fluctuate. This is normal.
When adding water from most municpal taps, the chlorine will off gas, which will also cause pH to change.

Best pH Range for Aquaponics

A healthy range of pH for most fish and plants is 6 to 7. Many plants and fish prefer certain ranges of pH. For this reason, some plants like roses and blueberries will not do well in an aquaponics systems. Also, macronutrients and micronutrients are absorbed by plants depending on what the pH is. Too high or too low and the plants will not be able to absorb the nutrients in the water.

How pH Relates to Aquaculture Breeding

pH also determines aquatic life breeding cycles. As pH changes so will the number of fish eggs that are produced, or if they can be produced at all.

Lowering pH in Aquaponics Systems

As you might remember lower pH is more acidic. Here are some safe additives you can use to lower the pH of your aquaponics system.

  • pH Down
  • Hydrochloric Acid 1 or 2 caps per 250 gallons
  • Acetic Acid (Vinegar)
  • Sulphuric Acid
  • Maidenwell media or Diatomite (5.2-5.8)
  • Iron sulfate fertilizer

Do not use citric acid – it is antibacterial and will kill your filter.
Note: if you have limestone as your gravel, you will constantly have low pH. Your sourcewater might also be the culprit if you top off with a non neutral pH. I’ve also read that injecting CO2 directly into the water might lower pH too.

Raising pH in Aquaponics Systems

Higher pH readings are called “base”. Here are some safe additives you can use to raise the pH of your aquaponics system:

  • pH Up
  • Dolomite Lime – Calcium Magnewsium Carbonate
  • Calcium Hydroxide (hydrated/builder’s/slaked/hydrated limes)
  • Potassium Carbonate (bicarbonate)
  • Potassium Hydroxide (pearl ash/potash)
  • Snail Shells
  • Sea Shells
  • Egg Shells

If you are using shells, boil, bleach or hydrogen peroxide them first to kill all bacteria. Containing chemicals/ingredients in a nylon stocking or other bag will allow you to remove it easily once you are below 7 pH.

pH Explains Cycling

Cycling aquaponics systems simply means that the nitrfying bacteria are present and the system is stable. By monitoring pH, you can tell what is happening or has happened recently in your system. Especially when starting an aquaponics system, record the pH regularly.

{ 8 comments… add one }
  • Sean May 24, 2014, 8:25 pm

    I have a new system and I’ve seen 2 different spikes, the first one was a ammonia spike, and the second was nitrites and nitrates . Since getting both under control my ph is a little high ( I think). It’s between 7.4-7.6. I would like to try the vinegar but do not know how much to put in. I have a 250 gallon tank with 200 gallons of water in it. Could you please give me the info I need . Thanks

  • filipposnik June 18, 2014, 8:34 am

    thank u for the info. i have a question: i have in my tank PH8 and i use CANNA PH DOWN to increase th level of PH. My question is, why the PH is stuck at 8 and dont go down? my plant are dying

  • Jay gamble June 23, 2014, 1:06 pm

    I work for an aquaponic farmer. He’s establishing his new plants in a trough system. The initial ph was taken and it measure d 8.3 pH. He is going to put citric acid in his system. It’s not connected to reverse flow into his fish tank. It circulates the trough water only. Is this prudent?

  • Wayne May 17, 2015, 9:27 pm

    My system consists of three grow beds 40″x48″x13″ I have a 250 gal fish tank with about 25 tilapia ranging from 13″ down to 6″. I have a 165 gal sump. My ammonia level is 0 ppm; nitrite level is 0 to 0.25 ppm; the nitrate level is 40-80 ppm and the PH is 7.6
    The system is only about a month old. I inoculated my system from a seasoned system. I planted a number of vegetable plants and while they are growing, they have become yellowish green much like iron deficiency. I assume the high PH is a problem. I don’t know if I should wait it out and assume as it matures the PH will go down; or should I begin to lower the PH? Or. Should I add cheated iron while I wait for the PH to drop?
    Any help you might offer would be appreciated.

  • mark October 9, 2015, 3:45 pm

    Concerning lowering pH.
    I noticed N-pHoric acid is not included in your list of recommended acids. Could you explain why?
    Thank you.

  • hugh gallen December 3, 2015, 8:59 am

    will the limes kill fish
    hugh gallen

  • Gessika February 21, 2016, 6:43 am

    nice video very nice video very informative and idiot proof and very nice of you to point out . thgins don’t go according to plan all the time like cutting holes and tub changing shape with water weight.

  • Gail Cochrane March 1, 2016, 5:02 pm

    I keep two aquaponics systems for a school district in Phoenix. Lately my pH readings are staying stubborn at around 7.6. I have been adding small quantities of muratic acid, around one ounce to a 600 gallon system every day for a couple of weeks. I have not had this problem before.

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