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.

The hardness of the water in the aquarium

The term "hardness" of water refers to the concentration, content, of calcium and magnesium in the form of ions in a given sample. with this term we refer to a total value, which can be divided into two others, the permanent hardness and the temporary hardness. The latter is missing after, for example, we boil our sample, in order to favor, through boiling, the elimination of the CO2 that makes up the calcium carbonate (in chemical terms Ca (HCO3) 2 + boiling = CaCO3 ( white solid) + CO2 (gas) + H2O (water)). during the boiling process the calcium carbonate is solubilized and remains, upon complete evaporation, on the edges of our container (limestone).
We are interested in the two hardnesses, and not their total sum, which take two names according to their characteristics: we will have GH which is equivalent to permanent hardness and KH which is equivalent to the measure of temporary hardness. The scale used, unlike the one commonly used by aqueduct technicians, is the German one. The reference that follows the result of our measurement will be:

for permanent hardness in German degrees = ° d GH

for temporary hardness in German degrees = ° d KH

these abbreviations are of fundamental importance to correctly refer to the two values, since if you speak to your aqueduct technician or to the technical office of your municipality to find out the quality of the water in your home, you must correct the value which is usually expressed in French degrees (° f).
This scale identifies various classes of water (total hardness)

The measurement of the KH value makes sense in fresh and marine water, while that of GH only makes sense in fresh water where the value is of fundamental importance for the correct growth of plants. The GH in sea water has values that are very, too high for our tests, and it is not practiced.
the correct values are different depending on the environment reproduced in fresh water, while the KH value should be around 8-10 ° dKH for the tropical marine aquarium.
The KH value for chemical correlations affects the concentration of carbon dioxide (CO2) dissolved in fresh water together with the pH. supplying CO2 to the system we can, at constant KH, reduce the pH value present in the aquarium, facilitating the breeding of some animals and the reconstruction of certain environments.

Chemistry defines salt water-soluble ionic compounds in the form of crystals. Once the crystal comes into contact with water it splits and breaks down into its main constituents: anions (negatively charged ions) and cations (positively charged ions). When completely dissolved in water, they increase its ability to conduct current.

Once the dissolution of the salt has been obtained, obtain a SOLUTION which is defined as a dispersion of the solvent (water, in our case) of the solute (salt crystals). The solvent is the substance in greater quantity, while the solute is the substance, in our case it is more correct to say the substances, in smaller quantities.

The CONCENTRATION (salinity) of salt is the ratio between solute and solvent and can be chemically expressed in different ways, what is normally used is called mixed percentage, as it expresses the quantity in grams of salt dissolved in a liter. So saying 35 g / l means dissolving 35 grams of salt in a liter of water, not as we read in some documents I found on the internet that indicate dissolving 35 g in 0.965 liters of water, which would be equivalent to dissolving 36 , 27g / l.

If we consider the different seas and oceans of the world it can be seen that there are differences in concentration between the different areas, for example the Mediterranean sea has a concentration of 38 g / l, the red sea about 40g / l, the ocean Atlantic 37.5 g / l, while if we consider an average value that always facilitates operations we find our beautiful 35 g / l.

The international scale for the measurement of salinity was established at the end of 1978 in order to have a world reference of marine salinity for scientific studies; the scale is called PSU (acronym for Practical Salinity Units) where the ratio is estimated through the conductivity of a seawater sample with that of the standard solution of potassium chloride at 32.4356 g in one kg of water at a temperature of 15 ° C. There is no unit of measurement and 35 psu correspond exactly to 35 grams in 965 grams of water, for a total of 1 kg. This measurement method is the one used by manufacturers of controller and automation systems for aquariums.

	Salinity sea Surface
	Salinity sea Surface from satellite

TEMPERATURE is another very important factor for our marine reef aquariums. Considering the preparation of synthetic sea water we cannot but talk about it. All the compounds of the synthetic salt for aquariums are chemical raw materials (raw matirials), i.e. they are the basic elements (sodium, chlorine, calcium, magnesium, etc.) mixed together in order to recreate the composition of natural sea water (Natural Sea Water - N.S.W.) which contains about 78 different elements. Each raw material has an optimal dissolution temperature and usually varies with increasing temperature (direct solubility).

DENSITY is another parameter on which a lot is always written and is one of the most controversial. This parameter measures the tenacity of the bonds between molecules, and varies as a function of the salt concentration and temperature. The density that normal aquarium instruments measure is the RELATIVE DENSITY (specific gravity) which refers the density of salt water to a sample of pure water at 4 ° C and to an atmosphere. the value we find on the scale thus indicates how many times our water sample is heavier than pure water. The value has no unit of measure or you can put the abbreviation of the measure SG. I often find arguments based on nothing that argue about. (period) or on the, (comma): will you read 1.026 or 1.026? The question, as mentioned, does not exist since the point in the Anglo-Saxon context is equivalent to our comma, while we use it to express the thousands; and then logically our sample will not be able to weigh 1026 times pure water. The other possibility is that we express ourselves in kg / m3 instead of in g / cm3 and therefore we write the point of thousands which could also be omitted. What I always care a lot about is that the other two fundamental values ​​Temperature and Pressure are placed together with the SG value. This is because, above all, as the temperature varies, the reported salinity value varies considerably.

You can get used to this simple UNESCO tools.

Bibliografia internet:

• Da Wikipedia:
  • salt (chemical),
  • Solution (chemical),
  • Concentration (chemical),
  • density,
• specific gravity
• Proprietà dell'acqua di mare - Dr. Sergio Cappucci and Ing. Damiano Scarcella
• Corso basico di metereologia - misure oceanografiche
• Unesco - ocenography