The concentration of the H⁺ ions

Let's start with the simplest explanation, the chemical one. In chemistry, pH refers to the concentration of H⁺ ions (hydrogen cations) present in aqueous solution. Opposite the pH scale is the pOH^- scale you will never hear of which measures the alkalinity of the aqueous solution itself. The sum of the pH and pOH scales gives as a result 14, the maximum value of both scales.

The pH expresses the concentration (molar) of the H⁺ ions and is calculated with an anti logarithm in base ten of the same therefore the

pH = -log ₁₀ [H⁺]

where [H⁺] expresses the molar concentration of hydrogen ions.

The scale goes from a "0" acidity value to a "14" value which expresses basicity, consequently the "7" value corresponds to the balance between the concentrations of H⁺ and OH^-.

What are we interested in knowing about pH? the main thing that is always to be taken into consideration is that the difference between a pH point involves an enlargement of the value of the ions by 10 times, which said it would not seem neuppure so much but if we put all the zeros in the right place we notice the difference : for example a value of 7 is equivalent to a concentration of approximately 10^-7 ions, while a value of 8 is equivalent to 10^-8 of ions. This difference is not tolerated by the animals if the change is sudden, and causes great stress to the animal, which if it fails to adapt can also succumb.

The pH in the aquarium
The pH also acts a lot on the metabolism and cellular activities of both plants and fish, the bacteria being very simple have greater ease in adapting to changes in pH. The pH value varies a lot from one place to another in the world, but also a lot from one point to another in the same stream or lake, so it is very important to know the most correct value for the plants and fish of the same environment. In fresh water we have animals that live in acidic waters such as those of the different catchment areas of South America, fish that live on the contrary in Africa that like higher pH like those of the great lakes Victoria and Malawi. In a marine environment, contrary to the variability of freshwater basins, this is almost invariable, whatever the sea considered. In a Mediterranean or tropical marine environment, the pH is about 8.2. It is ideal to keep this value stable but in the aquarium there are small variations due to the fluctuation of free CO2 and it ranges from 7.8 in the early morning to 8.5 shortly before the lights go out.

Check the value.
Checking the pH value is extremely quick and easy. However, there are many ways to do this. The most banal is litmus paper, a piece immersed in water changes color to be compared on a special scale, thus indicating the revealed value. In favor there is the low cost of the product, against the lack of accuracy in both reading and feedback on the scale. The colorimetric tests are those most used in aquarium. They are based like the previous one on the color change but are more precise, even if you have to do some to train the eye. There are also other more or less complex digital instruments that measure pH with the precision of two decimal places, too much for our use. In favor they have the precision, against the high but amortizable cost, and the continuous care that must be taken as cleaning and calibration.

Enjoy your reef.