Carbon Dioxide Makes Alkaline Water – Experiment

Written by Dr. Klaus L.E. Kaiser

Anyone can do this experiment and prove that carbon dioxide (CO2) increases the pH of natural water systems.

If you read the statements of carbon dioxide “war mongers”, including those from EPA, you are led to believe that CO2 causes acidification of water. That is true under aseptic conditions such as in a laboratory with distilled water, but not in nature. In nature, there are two crucial differences: the presence of nutrients and sun light. Together, they make a big difference as you will see for yourself by undertaking this simple experiment.

Lab testing

The Idea

The idea of this experiment is to prove that carbon dioxide in the atmosphere INCREASES the pH of water.

Supplies & Ingredients

You need:

  1. A transparent glass or plastic container (flask, container) with a tight-closing lid. [I am using one of those 1-quart plastic containers used in supermarkets for bulk food items, etc.].

  2. A small amount of common plant fertilizer. [I am using a 20-20-20 type all-purpose plant fertilizer].

  3. Distilled or de-ionized water, available in any drug store and most supermarkets.

  4. A way to measure pH of the water [I am using pH sticks; see also bottom note].

  5. A sunny place near your home (inside or outdoors).

  6. A few weeks of time.

What to Do

There is very little to do; the sun does most of the work. Also, please note all of the quantities and concentrations mentioned do not need to be exact; they are just general guidelines.

  1. Fill your container about two-thirds with the water. Keep the lid off and let it stand a comfortable temperature for a few days.

  2. Then measure the pH of the water. It should stabilize near pH 4.5 (weakly acidic).

  3. Add fertilizer at the appropriate rate for the amount of water in your container as per instructions by the manufacturer (commonly a teaspoon for 4 liters or a gallon) and stir until it is dissolved.

  4. Check the pH again; it should not have changed.

  5. Add a smidgen (barely visible amount) of soil, or pond algae as an inoculum.

  6. Tightly close the lid and place the container at a sunny spot.

  7. Wait a few weeks (say 3 to 6 weeks, depending on area, temperature and sunshine).

  8. Once you see obvious signs of algae growing in the container (discoloration of the dye coming with the fertilizer) and turbidity (slime or particles in the system), check the pH again. It will have increased to approximately pH 8.

  9. You have finished the experiment.


You will have demonstrated the conversion of carbon dioxide (from the air) together with the nutrients (the fertilizer you added) and sun light (radiation energy) to plant matter. Of course, nature does this all over without you doing anything at all. Minerals in rocks and soils slowly dissolve and the sun does the rest.

Initially, the distilled water contained no minerals and its pH was determined solely by the dissolution of carbon dioxide from air into the water. The resulting solution of carbonic acid has a pH of approximately 4.5.

Once you added the nutrients (plant fertilizer), added a smidgen of inoculum and waited a few weeks, things had changed dramatically.


The critical result of your experiment is the INCREASE in the pH of the water in your container from the initial 4.5 (carbonic acid solution) to the natural pH of 8 or higher. A pH value of 4.5 is definitely somewhat acidic and a pH of 8 is definitely somewhat alkaline (the opposite of acidic). This happened because the energy of the sun light allowed the algae to reduce the carbonic acid and form alkaline plant matter from it and the nutrients. That is why almost all natural water bodies (lakes, rivers, oceans) are alkaline (with a pH around 8) and not acidic, despite increasing atmospheric CO2 levels.

Contrary to what many people claim about the “acidification effect” of carbon dioxide, nature quickly turns it around and uses CO2 to produce organic matter that makes the water alkaline. The increase in pH was obtained from the conversion of an acidic solution of carbon dioxide and the nutrients with the help of the sun’s energy via the photosynthesis process to alkaline water. You demonstrated it yourself.

Oh, I almost forgot: Your experiment also produced an important by-product, namely molecular oxygen which we need to breathe to sustain life. You may have breathed in some of these molecules already.

Note regarding the pH measurement: It can be measured in various ways. If you have access to a scientific measurement device (via your children’s school, for example) that’s great. If not try to purchase some “pH sticks” (color indicator strips) which are available from various suppliers. Make sure they allow you to measure the pH range from 4.0 to 8.0 in 0.5 unit increments. If you have difficulties obtaining such, send me a self-addressed stamped envelope and I will mail you some.

Comments (5)

  • Avatar



    Quote: ” This happened because the energy of the sun light allowed the algae to reduce the carbonic acid and form alkaline plant matter from it and the nutrients.”
    Thus the algae makes the water more alkaline (using CO2 as a nutrient). This Conclusion is not reflected in your headline: CO2 makes water more alkaline.

  • Avatar

    Ferdinand Engelbeen


    Some parts are missing from this experiment: I don’t see a “blank” for comparison. Anyway, it is not the CO2 which makes the water alkaline, but the removal of CO2 by photosynthesis.

    In the real world, rivers which flow through carbonate rich rocks will be alkaline, but lakes like in Scandinavia enclosed in bare granite are slightly acidic and remain so.

    Further, while I don’t see any reason for panic, not for fish, neither for plankton or corals, the oceans are getting slightly less alkaline than a few decades ago. That was measured in a few fixed station series and regular cruises over many parts of the oceans.

    And last but not least, the reactions in your experiment indeed are working in the real world, but by far not enough to remove all CO2 that humans emit per year. See:
    The calculation of the net CO2 removal by the total biosphere is based on the production of oxygen…

    • Avatar

      John Marshall


      Ocean waters are at a pH level that is ”normal”, ie. 7.6-8.4 as quoted in text books on Oceanography. Levels measured at the lower end of the range are still within the natural range.
      There will be annual variations of ocean pH so date of measurement is important as is which hemisphere since there will be variations north and south.

      • Avatar

        Ferdinand Engelbeen


        Agreed, much depends of the seasons: increased biolife increases pH and opposite. But for the few fixed stations the trend is clear. See e.g.
        Unfortunately, they had a nice overview of the trends, but that is not anymore online. I did find the ALOHA trends of the fixed station in Hawaii:
        which gives the CO2 trends in air and water and the pH trend. Only one “error”: the plotted concentration of CO2 in water is not the real concentration (that is many times higher, including bicarbonates and carbonates), but the pCO2, the concentration in air when in equilibrium with the air above the water. As that concentration is lower than the real concentration in air, the oceans around Hawaii are sinks for CO2.

  • Avatar



    I’d replace the fertilizer with yeast in a solution to generate the CO2. Enclose both (CO2 via yeast and water) in a suitable semi-air tight container. Another idea, why not drop a chunk of dry ice in the water and seal it? Or, as in the yeast setup, add dry ice to the enclosure.

    I’d wonder about how the fertilizer would react with the water in addition to adding CO2…

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