Water ph test is produced by the industry in the form of strips impregnated with an indicator substance. These test strips are convenient. Their packaging has a scale for determining the concentration of hydrogen ions.
But these test strips are not always on sale. And the prices for them bite. This was the case at the time of writing this article (2012). Now you can order anything over the Internet and with the growth of competition the prices have become quite acceptable (2023). God only knows what will happen next.
pH meters with all their advantages also have a relatively high price. And if for a fish farm such a purchase is profitable and justified, for an amateur aquarist it may seem wasteful.
What should you do then? Homemade ph test strips will help to get an idea of the ph of the water in the aquarium. In addition, making them will be a great practice for young chemists.
Water pH test can be made from natural substances
In the article about hydrogen index we have already mentioned the fact that there are many substances in nature that change their color depending on the concentration of hydrogen ions. Tea becomes yellow instead of brown if you throw a slice of lemon into it. Borscht, in which beets have been boiled, will change its color from orange to bright red if a little vinegar is poured into it.
Also their color can change depending on the concentration of hydrogen ions – juice of mulberry, black currant, cherry. In general, there are several hundreds of such organic indicators in nature. We use one of such natural indicators to create our homemade test strips to determine the ph of water.
Cauliflower water pH test
И будем мы использовать вещество, содержащееся в цветной красной капусте. Красная цветная капуста содержит пигмент anthocyanin, который относится к группе флавоноидов. Он то и обусловливает цвет сока капусты и изменяет свой цвет в зависимости от кислотности.
Антоцианы имеют, как правило, красный цвет в кислой среде. И синий в щелочной. В нейтральной среде их цвет фиолетовый. Такими же свойствами обладает и упомянутый выше пигмент столовой свеклы.
Preparing raw materials
We will need half a cup of medium-sized red cauliflower. Cut it into small pieces. The smaller the better. Put the chopped cauliflower in an enameled pot and pour one liter of water. Put the pot on the fire and bring it to a boil. After our potion boils, let it simmer for another 20-30 minutes on low heat.
Some of the water will evaporate. You should get a deep purple (almost black) broth. After 30 minutes, take the cabbage broth off the heat and put it somewhere to cool down. While our indicator is cooling down we can start preparing the base for our tests.
What kind of paper to use as a base for the pH water test ?
It is best to use A4 printer paper for the test strips. Printer paper is coated. Therefore, firstly, it is white and will not introduce additional error due to color distortion. Secondly, it will well absorb the decoction of our indicator. The paper should be cut into sections of approximately one by five centimeters.
But before they can be used for ph determination, they must be soaked in an indicator solution. So we return to our cauliflower broth. During this time it has already cooled down and now it should be strained through gauze. The cabbage itself can be squeezed by wrapping it in the same gauze and twisting it like a tampon. The squeezed cabbage can be thrown away. You may not squeeze it and eat it…..
Impregnate the paper with the indicator
And in the cooled cabbage broth, which should have a rich purple (almost black) color, put the pre-cut printer paper. Make sure that the paper does not stick together and is evenly soaked in the red cauliflower broth. Soak the paper in the decoction for about 10 minutes. The paper should turn a pale lilac color.
After that, the paper must be dried. To do this, lay our products out on clean paper, or on the same printer paper. I find it easier to dry the paper by hanging it on a clothesline. Therefore, I cut the paper first into long ribbons about 1 centimeter wide. And only after soaking them in broth and drying them, I cut them into test strips about five centimeters long.
How to store the water pH test ?
After the paper soaked in cabbage broth dries – it is possible to carry out ph determination. Now the tests should be put either in a specially prepared box or in a polyethylene bag. The main thing is that the packaging should protect the strips from moisture.
How to use a homemade water pH test
It is easy to use homemade ph tests. Drop one to two drops of the test solution onto the test strip with a pipette. Allow one to two minutes for the moisture to dissolve the dry indicator and react with it. As a result of this reaction, the color of the paper will change depending on the ph of the water, which can be determined by comparing the color of the test strip with a color scale. The color scale is usually as follows.
If a different pigment is used as an indicator, the color scale will be different from that shown here.
Color scale for our water pH test
You can either print this picture on a printer or make (draw) the scale yourself. To do this, cut a rectangle from white drawing cardboard with dimensions of 1 by 15 centimeters and divide it into 14 parts. In other words, draw transverse divisions through each centimeter.
Take colored pencils (or felt-tip pens). Shade in red the distance from one to four centimeters; in crimson the distance from four to eight centimeters; in purple – from eight to nine; in blue – from ten to eleven; in green – from twelve to thirteen; in yellow – from thirteen to fifteen. The yellow color our indicator does not show.
Color scale calibration
To calibrate the color scale, you can use a number of substances that have a constant ph of the medium in their original form. Below is a table of such substances, from which you can choose the most available to you.
|Some pH values
|Lemon juice (5% citric acid solution)
|Hand soap (greasy)
|Concentrated alkaline solutions
This table will also be useful if you want to experiment with any other natural indicator. After all, you can make test strips from blackcurrant juice, mulberry juice or beet decoction using the method described above.
Accuracy of the water pH test
Of course, when making test strips at home in the technology will interfere with various errors that can affect the accuracy of the concentration of hydrogen ions. Therefore, before using a new batch of homemade test strips, it is advisable to check their readings with substances with a known acidity value given in the table above. Or with the help of more accurate methods of measuring the hydrogen index (pH meter, acid-base titration).
Any method of measuring physical and chemical quantities is subject to errors in the readings. Our strips may not be the most accurate. But they will always give a clear picture of the pH of the water in your aquarium or any other liquid medium.
The method of making the indicator described here is very simple and is taught to young chemists. Of course, it is not perfect. And manufacturing errors can also distort the readings. Nevertheless, for our use it is important that the pH of the aquarium water remains close to 7. The acidity of the water in the aquarium can change due to the activity of fish and it is advisable to check it once a week. Especially if the aquarium is overpopulated.
Despite the simplicity of the method, if you use the substances from the table above to calibrate your test strips, you will not miss a gross change in the ph environment in the aquarium. And in time to take appropriate measures that will save your pets from trouble, and you from disappointment.