Aquarium water

How to raise or lower the pH of the aquarium

Aquarium water 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. The choice will entail that the quality of the water responds to a certain chemical composition , in which the pH is within a limit band, both above and below. Depending on the species of fish in our aquarium, we will need a different pH level. Our mission is to keep the alkalinity or acidity of the water within acceptable parameters, but… What to do when we need to raise or lower the pH of the aquarium?

What is pH?

PH is short 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 is the aquarium pH measured?

The pH has a scale that goes from 1 to 14, with 1 being the most acidic value and 14 being the most alkaline. The neutral value is right in the middle, 7.
In the market we will find two ways to measure the pH of water:

  • Potentiometer or pH-meter
    The pH-meter is an instrument that measures the potential difference between two electrodes, a reference one that is usually silver or silver chloride, and a hydrogen ion sensitive glass electrode. Discover HERE the best digital pH meters.
  • Acid indicators (Colorimetric system)
    This is the usual way in which we normally measure 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 used the pH meter, although sufficient for our objective.
    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, by adding a few drops to a sample of aquarium water, it will turn a certain color, which we can contrast with a coded color wheel. Discover HERE the best Aquarium tests.

The organisms that live 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?

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

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

How to lower the pH of the aquarium?

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 have to consider the possibility of 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 specific event, then we can resort to removing part 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 an element that destabilizes the pH, such as coral aquarium sand . If this is the problem, it is best to remove it and use silica sand.
  • Check that you do not have 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 is because it has limestone content, it is best to remove these stones. Look for aquarium stones that do not alter the composition of the water.
  • Adding wooden logs, especially mopani, help lower the pH of the aquarium and make the water more acidic.
  • Breathe CO2 into the aquarium, since carbonic acid lowers the pH and also benefits the cultivation of plants in the aquarium, accelerating the photosynthesis process.
  • Add commercial acid buffers.
  • If the problem is constant, one option is to use peat to lower the pH.

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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 lower than 4 and a very low hardness (gH).
The reason is very simple, as they pass through the subsoil they cross masses of peat , which give them these physical characteristics and in many cases, also a certain yellowish coloration.
In the aquarium we can achieve something similar, making the aquarium water filter through the peat … Be careful! Gardening peat , which can carry fertilizers and plant protection products, is not worth it .
There are several ways to use peat in the aquarium:

  • One of them can be to add peat to the substrate of the aquarium , so that it is always present and in contact with the water.
  • Another option is to add peat to the aquarium filter , so that, by mechanically filtering the water, we induce the water to filter through the peat.
  • Other aquarists prefer to make a kind of tea out of peat. The peat is introduced into a bag (such as a pillowcase) so as not to have to filter the water, it is put into the water that we are going to use to make the changes to the aquarium, and it is left to rest 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?

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

  • Perform partial water changes, 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 coral sand or if the problem is specific, putting calcareous material in the filter, such as coral, cuttlefish or shells. They can also be inserted into the aquarium directly, but in such a way that we can remove them when they are no longer necessary.
  • As before we had to remove the calcareous stones, if we have any we can introduce them into the aquarium.
  • Commercial buffers, such as salts or pH enhancers.
  • Add 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 levels that we need to raise.
It is convenient to make a solution of the product in water. Subsequently add the product little by little and not suddenly increase all the degrees that we need, so as not to stress the fish.
To raise the Kh one degree 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.
You are probably a little checkered, if we are talking about pH and I skip with the Kh or » temporary water hardness «.

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Kh as a buffer or pH regulator

There is a very close relationship between the pH of the aquarium and the Kh, so that if we want to have a stable pH, we also have to control the Kh.
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 track of the two together:

  • KH less than 2 ° reveals little carbonate presence. 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 optimal so that the PH remains 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.


Maintaining a stable pH is necessary for the quality of the aquarium water , and the life of our fish.
More than going up or down, the really important thing is the stability of the pH, that is why we have to carry out periodic measurements of the water, at least once a week.
As I think it has been clear throughout the article, all the parameters that affect water quality are closely related, and sometimes it can be exasperating… when that happens, there is an imbalance somewhere. We must find out what it is, to modify or remove it.
I hope this article has been helpful.

Water quality in the aquarium

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