Let’s talk about the pH of the water

Fish care

Without going into too much technical data, being more practical, we will define the pH as the “quantity” of H + ions that are dissolved in the water in relation to OH-

In pure water there is a concentration of H + equal to that of OH- and we say that it has a pH of 7 (neutral).A concentration of H + higher than that of OH- results in a pH below 7, which we call acid waters. A concentration of H + lower than that of OH- results in a pH above 7, which is called alkaline or basic waters. Acidic water is associated with corrosive processes and alkaline water is associated with calcareous incrustations.


The most important fact of this reaction is that the pH is expressed as a “negative logarithm in base 10” … but, what  does this mean … because in a water of pH 7.0 the H + concentration is 10 times higher To a pH 7.1.,  a minimum variation is a great change in the characteristics of the water.

This has a great repercussion in our aquarium and in our fish that we will try to demonstrate:

Fish exchange liquids through the skin through a process of osmoregulation, in which the ionic value of water is super important.

If we look at the different tabs of each species in the specialized atlases that exist on the internet we will observe that for each of them there is an advised range of pH, suitable for the correct maintenance of these fish.



A good reference of the optimum pH for each species gives us a series of very important data:

-They serve to know what their “genetic demand” is: fish have morphology adapted to each type of water, so that although its provenance is not wild, we can know for what type of water are “designed”, this is important. Yes it is true that this should not become an obsession.



-It is useful to know (or have more data) to know which fish are compatible with which others: it is easy to suppose that if one species has exactly the same requirements as another, they come from the same area, etc … they can be compatible among them. There are many exceptions, for example in cases of predatory species of other, aggressive fish with other fish of the same species, etc.



But it is very important to point out a couple of ideas and tricks that will help us to properly maintain our fish:

-Tap water has a pH (as a rule) of between 7.2 and 7.8.

-Osmosis water has a pH (as a rule) of between 5.8 and 6.6.

-Obviously if we mix two waters of different pH’s will give us an intermediate result.

The worst thing we can do for our fish is, obsessed with having a particular pH, forcing the pH to rise or fall sharply (for example with chemicals), these fluctuations in pH concentrations pose a shock to fish, sometimes fatal.




As a general rule, it is much more interesting and safe to have an intermediate pH (from 7.0 to 7.6) for any type of fish that we are constantly raising and lowering this value.

As both the pH value of the tap water and the osmosis machine (with continued maintenance) are quite stable, it is best to establish that the mixture may be adequate to obtain our desired value: for example 50% tap water PH 7.4 and 50% osmosis water to a pH of 6.6 … we would have as a result of that mixture a neutral water near pH 7.0.

Our advice is to calculate what is the right mix and in each weekly water change always respect that proportion, which will give you a stability that is more important than the exact adjustment of the pH value to the natural requirements of the species. A good way to know the pH of the water is using a table withthe information or using some instruments we can acquire in the pet shop.

It should be remembered that practically 100% of freshwater species currently marketed on a regular basis are bred in captivity, in most cases the water in which they are maintained are relatively high pH waters, the ones they are adapted to.




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