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The pH in aquarium – for beginners

Today we will talk about pH, which certainly is one of the most basic but necessary for each aquarium, both marine and freshwater. The pH is a value ranging from 0 to 14 and measuring the acidity of the water when its values ​​are between 0 and 7, while it is referred to the basicity of water when they are between 7 and 14. An equal value 7 is considered neutral. Wanting to make further clarification, within the range of values ​​between 0 and 7, the lowest values the more acidic is high and not the other way round. While for the basic values, the more the pH is high and the more it is alkaline (or basic).

In our freshwater aquariums, the ideal pH for most fish is close to neutral values, i.e. around 7, with a slight tendency towards acid, so between 6.8 and 7.2, while in the marine tanks we should instead have a pH between 8 and 8.4.

This is very important because outside of these values ​​the water could cause serious damage to our fish. Even sudden pH swings can cause stress, illness, and death to the living beings of our tanks. For this reason, especially for beginners, it is essential to keep an eye on the pH values ​​of your aquarium, just like you do with the temperature, and do so with a certain frequency so that you can intervene if these values ​​are out of the ideal range or undergo any swings.

Why does the pH change?

pH can change for many factors such as water movement and its gas exchange, increase or decrease in carbon dioxide, accumulation of organic and nitric acids. Due to these factors often in salted water, the pH tends to fall while in fresh water it tends to rise for example due to carbon-depleting plants (for chlorophylline photosynthesis), thus increasing pH suddenly.

PH, CO2 and KH relationship

Before explaining how pH is controlled we have to understand that there is an important relationship between pH, CO2 and KH (carbonate water hardness). In fact, controlling the amount of CO2 (or carbon dioxide) and the value of KH, it is possible to influence pH. With a little imagination we can imagine CO2 and KH as two people who are moving a heavy object, pushing in the opposite direction, ie one against each other and where the object moved is the pH. Obviously when these two hypothetical forces applied to push are in balance, the object does not move, that is, we have a constant pH. Instead increasing and decreasing one of the two forces, the pH will move accordingly. For example, if we increase CO2 and decrease KH in our aquarium, we will have a decrease in pH. However, I note that it is best to act on both forces rather than on one. To better understand this statement, let’s go back to our example: it’s never a good idea to let both the people push the object at same time, trying to overwhelm the other. In fact, if one of them simply decreases the thrust force, the other one can move the object with a much smaller effort! For this reason, instead of enormously increasing the amount of CO2 it is advisable to lower the KH.

But in practice how do you control the pH?

There are various methods for directly controlling the pH, as stated in the paragraph above about the relationship of these elements.

Normally to decrease it, which is particularly useful in fresh water, small bubbles of carbon dioxide (CO2) are injected in our tank. More bubbles are injected and the more pH is lowered. Finally, as mentioned above, we should try to find a right amount of bubbles per minute so as to create a balance and make the pH constant.

Other methods, most commonly used in freshwater aquariums, are to add turf into the filter or add RO water. To increase the pH you can simply increase the movement of water with pumps. The movement favors the expulsion of CO2 and therefore a rise in pH. Another method is to increase KH by introducing calcium carbonate (CaCO3), by means of a calcium reactor (also useful for corals), with calcium supplements or a kalkwasser reactor.

How do I monitor the pH?

Typically, you can use simple and cost-effective kits consisting of a glass tube where aquarium water is collected, a small container with chemicals to be inserted into the test tube, and finally a colored table to facilitate pH measurement. Alternatively, electronic testers can also be  used, with a probe always immersed in water and an electronic display that shows the pH value.

Simone Grimaldi
Simone Grimaldi
Appassionato di informatica ed elettronica sin dall'infanzia, sempre in deficit di conoscenza, ho trovato in questo affascinante universo dell'acquariofilia l'argomento che riesce a stimolarmi ma mai a saziarmi abbastanza da diventare noioso!

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