raise or lower the pH of the aquarium

How to raise or lower the pH of the aquarium

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The water in the aquarium is the main element on which life develops. When we talk about the quality of the water, we are not talking about a single quality, but the one necessary to reproduce the biotope we have chosen, learn how to lower and raise the pH in aquarium for the fish to thrive and survive

The choice will imply that the quality of the water responds to a certain chemical composition, in which the pH is within a limit range, both above and below.

Depending on the species of fish in our aquarium, we will need a different pH level. Our mission is to maintain the alkalinity or acidity of the water within acceptable parameters, but… What do we do when we need to raise or lower the pH of the aquarium?

  • what is pH level
  • several ways to lower the pH level
  • several ways to raise the pH level
  • kH as a buffer – what is

What is pH?

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pH is the abbreviation for hydrogen potential. When we talk about the pH of water or any solution, we are talking about its degree of acidity or alkalinity, which is determined by the amount of hydrogen ions that are present.

You will see that whenever we talk about the pH of the aquarium, the term is expressed in degrees.

How do you measure the pH of the aquarium

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the pH scale

The pH has a scale from 1 to 14, with 1 being the most acidic and 14 the most alkaline. The neutral value is right in the middle, 7.

There are two ways of measuring the pH of water on the market:

Potentiometer or pH-meter

lower pH in Aquarium

The pH meter is an instrument that measures the potential difference between two electrodes, a reference electrode that is usually made of silver or silver chloride, and a glass electrode that is sensitive to the hydrogen ion.

Acid Indicators (Colorimetric System)

This is the usual way in which we normally measure the aquarium water, with those strips that react to pH, gH, nitrite, nitrate and ammonia levels.

You can also find it in liquid solutions, with a pH-only test kit.

The measurements are approximate and not as reliable as if we use the pH-meter, but sufficient for our purpose.

The mechanism is simple, the strips are impregnated with weak acids or bases, which react with a different color depending on the acidity or alkalinity of the water.

In the case of liquid solutions, when a few drops are added to a sample of water from the aquarium, it will turn a certain colour, which we can contrast with a colour-coded wheel.

The organisms living in the aquarium, both fish and plants, are sensitive to sudden changes in pH, so it is important to measure the pH every week.

What is the ideal pH for my aquarium?

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The ideal pH for your aquarium will depend on the species of fish you have.

  • The recommended pH for inland species is between 6.5º and 8.5º.
  • Amazonian species live in what is called black water, with soft water. In this case the recommended pH should be more neutral, between 6º and 7º.
  • The fish that come from East Africa prefer a slightly more alkaline pH, between 7.5º and 8º.

How to lower the pH of the aquarium?

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The first thing we have to do to know how to lower the pH of the water in our aquarium, is to measure the pH of the water we use to fill it…usually from the tap

  • If the pH of the tap water is already high, we must consider installing a water softener or a reverse osmosis unit, which will provide us with ideal water for the aquarium.
  • It may be the case that the rise in pH is a one-off event, so we can resort to removing some of the water from the aquarium, adding a mixture of tap water with distilled water, which fluctuates between 5.5º and 6º.
  • Another possibility is that we have introduced some element that destabilizes the pH, as is the sand for coral aquarium. If this is the problem, it is best to remove it and use silica sand.
  • Check that you do not have any limestone rocks in the aquarium, which can also be a reason for the pH to rise. To check if the rocks have traces of limestone, take a rock and spray it with salfuman, if it bubbles, it has limestone content, it is best to remove those rocks. Look for aquarium rocks that do not alter the composition of the water.
  • Adding wooden logs, especially mopani, helps to lower the pH of the aquarium and make the water a little more acidic.
  • Inject CO2 into the aquarium, as carbonic acid lowers the pH and also benefits the cultivation of plants in the aquarium, accelerating the process of photosynthesis.
  • Adding commercial acid buffers.
  • If the problem is constant, one option is to use peat to lower the pH.

How to use peat to lower the pH of the aquarium?

The water that can be found in virgin forests has an acidic pH, even below 4, and a very low hardness (gH).

The reason for this is very simple, as they pass through the subsoil they pass through peat masses, which give them these physical characteristics and in many cases also a certain yellowish colouring.

In the aquarium we can achieve something similar, making the water of the aquarium filter through the peat… Watch out!! It is not worth the gardening peat, which can carry fertilizers and phytosanitary products.

There are several ways to use peat in the aquarium:

  • One of them can be to add peat to the aquarium substrate, so that it is always present and in contact with the water.
  • Another option is to add peat to the aquarium filter, so that when the water is filtered mechanically, we induce the water to filter through the peat.
  • Other aquarium-philes prefer to make a kind of tea out of the peat. The peat is put into a sack (such as a pillowcase) so that the water does not have to be filtered, it is put into the water we are going to use to make the changes to the aquarium, and it is left to stand for 1 to 2 weeks. Ideally an air pump should be used, which moves the peat into the water.

How to raise the pH of the aquarium?

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Just as we may find that we have a high pH and need to lower the pH of the aquarium, the opposite option may be given, that we have a low pH and need to raise the pH of the aquarium.

We have several options to raise the pH of the aquarium:

  • Make partial changes to the water, as long as the tap water has a higher pH. In the previous case we used tap water mixed with distilled water with a very low pH, in this case as we want to raise the pH, what we will do is introduce water with a high pH.
  • Use coral material. It can be coralline sand or if the problem is punctual, putting calcareous material in the filter, like the coral, cuttlefish or snails. They can also be introduced directly into the aquarium, but in such a way that we can remove them when they are no longer necessary.
  • Just as we used to have to remove the limestone, if we have any, we can put it into the aquarium.
  • Commercial buffers, such as salts or pH-enhancers
  • Adding potassium carbonate or potassium bicarbonate

How to raise the pH with bicarbonate?

A homemade trick that we can easily use is to add potassium bicarbonate, in the necessary amount, depending on the pH degrees that we need to raise.

It is convenient to make a solution of the product in water. Then add the product little by little and do not raise all the degrees we need at once, so as not to produce stress in the fish.

To raise one degree of Kh using sodium bicarbonate, use 3 grams per 100 liters, in the case of potassium bicarbonate, use 3.6 grams per 100 liters to raise one degree of Kh.

Probably you are a little checkered, if we are talking about pH and you jump with Kh or “temporary water hardness”.

Kh as a buffer or pH regulator

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There is a very close relationship between the pH of the aquarium and the Kh, so if we want to have a stable pH, we have to control the Kh as well.

With a high Kh level, the aquarium water will be stable and it will be easier for us to control the pH.

Kh and pH show the following relationship, and that is why it is important to keep control of both together:

  • KH less than 2º reveals little presence of carbonate. The pH is unstable, changes from very acidic to very alkaline water can occur quickly.
  • KH between 2º and 4º, the presence of carbonate is the optimum for the PH to remain slightly acidic, around 6.5.
  • KH between 4º and 6º, offers ideal carbonate readings to stabilize the alkaline PH between 7 and 8.
  • When the KH is higher than 6, it shows a high presence of carbonates, being able to maintain an alkaline PH higher than 8.


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Maintaining a stable pH is necessary for the quality of the aquarium water, and the life of our fish.

More than just going up or down, what is really important is the stability of the pH, which is why we have to take regular measurements of the water at least once a week.

As I think it has become clear throughout the article, all the parameters that affect the quality of the water are closely related, and sometimes it can be exasperating…when that happens, there is an imbalance somewhere. We have to find out what it is, in order to modify it or eliminate it.

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