Acidity of Aquarium Water

pH – Acidity of aquarium water.

It is well known that a water molecule consists of two hydrogen atoms and one oxygen atom – H2O. However, not everyone remembers that molecules in a solution are not in an intact state, but in the form of ions – positively and negatively charged particles. This phenomenon is called dissociation. The degree of dissociation of water molecules is called the active reaction and is measured by the value of the hydrogen index, equal to the degree of concentration of H+ ions, taken with the opposite sign. For pure water, this value is 7 and is designated as pH 7. The Latin letters pH are read and mean pondus hydrogenii.

pH is the most important characteristic of water; this parameter represents the concentration of hydrogen ions in water and determines the acidity of the medium. If hydrogen is one of the products of dissociation during the reaction, the water acquires acidic properties. Alkalinity is the total content of negative ions that neutralize hydrogen ions when acid is added to the water. Water of different origins has different pH parameters. Its ideal values for an aquarium are between 6 and 9 units. Water in most fresh natural reservoirs has a pH from 5 to 8; more acidic swamp waters with a pH of 4.5 or their antipodes – alkaline lakes with a pH of 9-11 – are very rare. Environments with pH < 4.5 and pH > 9.5 are biologically aggressive and should be considered unsuitable for the life of aquarium inhabitants.

Sudden jumps in pH are especially dangerous; they are atypical for natural conditions, but can occur in an aquarium under certain circumstances. In nature, a smooth decrease in the hydrogen index and hardness corresponds to the rainy season and river flooding, which, along with an increase in shallow water temperature, encourages fish to spawn. On the contrary, an increase in pH and hardness is typical for dry seasons, when conditions in the river are rather harsh. Since the pH value is a logarithmic quantity, a change in pH by 1 unit means a 10-fold change in the concentration of hydrogen ions, by 2 – 100 times, etc.

A rapid (several tens of minutes) change in pH by 2 units with high probability will lead to irreversible changes in the gills of fish and their gradual destruction. Having experienced such trouble, fish can die, and sometimes this happens not immediately, but after a few weeks. Here, the different sensitivity to pH changes both in various fish species and in individual specimens within a species takes effect.

The pH value in an aquarium is not stable; it changes all the time. The pH indicator can be extremely dynamic and noticeably change in the aquarium during the day. The values of the active reaction of water freshly poured from the tap, settled water, and aquarium water taken for testing in the morning and evening can differ greatly from each other. Therefore, once having measured the pH value of water taken from the tap, one cannot assume that this value is established once and for all for your entire aquarium setup. These fluctuations are especially noticeable in soft water with negligible carbonate hardness. It is advisable to periodically test the pH level to avoid its sharp increase or decrease – both of which are fatally harmful to living creatures living in water. It is important to avoid sharp pH fluctuations.

During the day, pH can fluctuate by 2 units or more, so it is ridiculous to read in some aquarium manuals: “These fish need a pH of 6.0-6.3” – such precision can only be obtained in a small spawning tank without plants. In an aquarium with aquatic plants, such pH stability is completely excluded. The fact is that the pH value is influenced by such factors as the presence of free carbon dioxide, which is a metabolic product of both fish and plants, and the dissociation of organic acids contained in the water in one amount or another.

In hard water, the water reaction is more alkaline and acidity drops are smaller than in soft water. Soft water drastically changes acidity with the addition of a small amount of acid or alkali. Soft water with a low bicarbonate content has an unstable pH value. Moreover, in real practice, alkalinization of water is extremely rare, whereas lowering the pH below the allowable level is very easy to get.

An increase in the amount of CO2 or a decrease in KH makes the water more acidic; an increase in KH or a decrease in CO2 makes it more alkaline. Therefore, under prolonged bright lighting with a large amount of plants intensively absorbing carbon dioxide, the pH value can rise to 9. And at night, due to the lack of photosynthesis and the release of CO2 by plants and fish during respiration, it can drop to 6, which is unfavorable for the aquarium population. In an aquarium without vertical water circulation (from aerators and filters), the high pH in the upper layers can cause the destruction of plant tissues. The more blue-green algae, the more alkaline the environment. To reduce sharp fluctuations, mandatory night aeration of the water with air is recommended, which will sweep away carbon dioxide.

But remember that any changes in the pH level should be made smoothly and gradually! We note that buffering and alkalinity are closely related, because in fact, alkalinity is a buffer that slows down the change of pH in water. Poorly buffered water (low kH or temporary hardness) will be more prone to sudden pH fluctuations than well-buffered water. A substrate containing a lot of limestone can be considered a buffer to maintain high water hardness. Also, a piece of wood or driftwood can act as a buffer, which acidifies the water and lowers the pH. As a rule, hard water usually has an alkaline composition (pH>7) and is a good buffer. At the same time, soft water (pH<7) is somewhat more acidic and is not suitable as a buffer.

Fish, first of all, prefer to live at a relatively stable pH value. What exactly this value will be is not very important to them. Almost the overwhelming majority of freshwater fish, after a short and simple adaptation (unless we are talking about adapting fish straight “off the truck”), easily adapt to life in water with a pH ranging from 6.0 to 8.5. But this value must be relatively stable during the day, and if any changes occur, no more than half a degree per day. Fortunately, the tolerance of fish to their habitat is very high. And all these extremophiles live wonderfully in our ordinary water.

And now let’s note that the specified range from 6.0 to 8.5 includes the water of almost all regions of our country and neighboring regions. If you have water flowing from the tap with a pH value in the range of 6.5-8.5, then you do not need to specially prepare water to keep any fish. We repeat that in this article we are talking exclusively about keeping fish, without touching upon the issues of spawning, when sometimes it is really necessary to scrupulously formulate water with strictly defined parameters. But what should aquarists do if their water still does not fit into the specified framework? First, let’s look at the harmful manifestations of suboptimal pH values.

In excessively soft and acidic water, the acidity itself acts abiogenically first of all. As the medium acidifies, damage to the outer integuments and eyes appears first, then due to burns, dysfunction of the gill lamellae begins, and the internal organs, primarily the kidneys, are affected last. Also, in an acidic environment, carbon dioxide poisoning is possible, the limiting concentration of which in this case can exceed 140-150 mg/l.

But most dangerously, in the absence of a bicarbonate buffer, the pH of the medium can change, and very sharply and spasmodically, and this happens again in the direction of acidification. Most often, this is caused by the gradual accumulation of fish metabolic products in the water. A decrease in pH and water temperature leads to a decrease in ammonia toxicity, but at the same time, the efficiency of bacteria processing ammonia drops. The optimal conditions for them are neutral water (pH about 7) and a temperature of about 30°C. At a pH below 5, their activity practically ceases.

In excessively hard and alkaline (pH above 9) water, everything is also bad. Firstly, with an increase in water alkalinity, an increasing amount of ionized ammonium turns into pure ammonia dissolved in water. Ammonia is many times more toxic than ammonium, so with seemingly minor increases in ammonium concentration, a severe poisoning of the entire aquarium can unexpectedly occur. Preventing this is simple – you need to change the water more often. Or use special water conditioners. Secondly, as the alkalinity of the medium increases, the oxygen assimilation in fish deteriorates. In an alkaline environment, a fish can suffocate even with what seems to be a sufficient oxygen content in the water. And of course, alkaline water itself (especially with a sharp increase in pH) causes burns and damage to the external organs of fish.

What to do?

And finally, the age-old question: what to do? In the case of very soft and acidic water, it is more difficult for aquarists; they constantly need to regularly monitor the pH indicator to see if the water has gone sour. For complete success in keeping any fish, it is advisable for them to increase carbonate hardness and reduce acidity, bringing it to neutral. And this is much easier to do than to soften hard water. Many fish, invertebrates, and plants need a specific pH value. Therefore, try to acquire such inhabitants for your aquarium whose water acidity in your region suits them.

Fish adaptation to existing conditions is necessary. First, let’s remember another simple and important rule: any fish adapts much easier when moving from harder and more alkaline water to softer and more acidic water, than vice versa. Without any problems, you can transfer fish within 20 minutes from water with dH 20° and pH 8.5 to water with indicators of dH 6-10° and pH 6.5-7.0. Remember, fish bred and kept for a long time in hard and alkaline water have a much higher immunity than fish living in acidic and soft water.

With sudden changes in pH values, not only fish, but also plants can die. Plant death usually occurs when replacing old water with fresh water, as well as in spring and summer, when aquarium lighting increases, especially with direct sunlight. The hydrogen index of aquarium water has a significant impact on the life activity of aquarium fish and plants. More complex plants are difficult to keep precisely because their lower and upper pH barriers are slightly separated from each other – after all, in running waters in their homeland, there are no such pH jumps as occur in aquariums with standing water. In plant tissues, pH shifts lead to a slowdown in photosynthesis and other biochemical processes, and at critical values, tissue necrosis and chlorophyll breakdown are observed.

It must be particularly emphasized that fish and plants can experience severe stress, chemical damage, and significantly weaken even with very short-term fluctuations in the pH level in the aquarium. Therefore, before choosing fish and plants for the aquarium, you are obliged to make sure that their requirements for aquarium water parameters, including pH, coincide. With a large number of plants in the aquarium, it is very good to know the acidity value in the morning before turning on the light in the aquarium and in the evening before turning it off.