Unfortunately, poor water quality makes fish susceptible to disease. It is difficult to identify fish diseases in an aquarium, however behaviour such as fish scratch, excited behaviour and even sudden drastic changes to the appearance of the fish. Therefore it’s wise to learn about the possible diseases that may occur in your fish because this may help you to recognize them in the future. Today we are going to show you alkalosis- A fish disease caused by ph fluctuations or “inappropriate pH”.

You often hear conversations with aquarists about cases of inexplicable massive fish death or “tank crashes”. Such cases most often took place in heavily overgrown aquariums with prolonged exposure to direct sunlight. As a result of increased photosynthesis, plants took up carbon dioxide from the tank water. When it was gone, they started absorbing calcium bicarbonates and finally calcium carbonates from the tank water. So there were no factors creating the highly acidic pH way above the preferred range of most aquatic animals. As a result, an alkaline pH was created, even exceeding the pH level 9 which is very dangerous for fish health.


This common disease is caused when the aquarium water ph increases above the level of 9 or 10. This event can occur suddenly (pH levels change rapidly) or over a long period of time (ph level changed gradually).

In the first case, fish usually start behaving strangely right away and show disturbing signs such as flicking themselves against the aquarium decorations or beginning to breathe heavily.

In the case of the latter, the symptoms of the disease may appear after a longer period of time or only when fish keepers introduce new fish into the aquarium or keep adult fish with a weakened immune system in it (the remaining fish may, to some extent, adapt to new conditions).

Very often, the symptoms we associate with high ammonia levels are the same as the symptoms of alkalosis. This is because in aquariums with a high concentration of alkaline, the process of converting ammonium ions into toxic ammonia takes place.

Circumstances favourable to the development of Alkalosis disease

-the use of decorative elements in the form of shells, limestone, calcareous substrate or other minerals is known to increase ph and general hardness of the water.

-abundant planting with the use of intense lighting


-reduced content of carbon dioxide dissolved in water

-poor water buffering capacity


Symptoms of alkalosis can be different in different species. The fish afflicted with the disease display clumsy behaviour and muscle spasms may be observed. Additionally, you can notice the accelerated movement of the gill covers and the swimming of the fish just below the water surface. Sometimes fish jump out of the tank water. Some fish scratch themselves against decorations in a flicking movement. Fish suffering from Alkalosis become lethargic, lose appetite and secrete more mucus. Sometimes fish’s skin becomes cloudy.


After finding too high pH in our aquarium, we must take steps to stabilize ph straight away. The main task is to eliminate the cause that led to this condition (e.g. too many limestone aquarium decorations that constantly discharge dissolved minerals). Then, after careful checking of all water parameters (mainly pH levels, water hardness, nitrates, nitrites and ammonia), we should systematically do the partial water change (up to two times a day for 30%)in order to reduce the ph levels.

After each water change, we check the pH levels of the water, along with the other parameters. An increased level of dissolved oxygen in the water is vital during this time to increase the health of the fish.

The new water that we replace should be neutral (pH = 7). Since the immune system of our fish has weakened significantly, it is advisable to use appropriate vitamin and water treatment preparations. The introduction of fresh nitrifying bacteria will allow your aquarium to replace the lost bacteria during water changes. If we do not struggle with the high alkalinity of the water (generally carbonate hardness), we can try to acidify the water by using carbon dioxide. The addition of Indian Almond Leaves or similar products can assist with providing a healing enviroment. The tannic acid released by leaves will help to prevent bacteria and can also calm fish down by creating a more natural appearance. Afterwards, this can be removed by adding a small bag of carbon to your filter. During the treatment period, keep in mind that fish are more sensitive to parasites and bacteria. In the event of damage to the gills of the fish, euthanasia should be done.


In order to prevent the environmental factors causing alkalosis fish disease, necessary preventive measures are essential. We must recognise that we are water keepers over and above fishkeepers. control the water parameters and do the regular partial water change and your fish will almost look after themselves. Moreover, newly bought fish should be kept in water with the same pH in which they have stayed so far and gradually change this pH (with an intensity of 0.3 points per day). Learn about quarantine aquariums with this helpful article.

Additional information

Depending on its composition (mainly the number of bicarbonates, carbonates, hydroxides, silicates, phosphates: calcium, magnesium, iron, manganese, sodium, potassium – i.e. alkalinity), water has a different buffer capacity. If the water has the appropriate alkalinity (simply carbonate hardness – these are only calcium and magnesium bicarbonates and carbonates), its buffering capacity can absorb and neutralize the added acid without significantly changing the pH levels.

In other words, the higher the alkalinity, the more stable the water is (it is less susceptible to changes in the pH of the water caused by intensive photosynthesis of plants, application of CO2 or the use of peat). If we have water with high alkalinity and we struggle with high pH, ​​lowering it with chemical acids or other means for this purpose (available in pet stores) is pointless (the buffer will neutralize the acid, and the pH will not move).

If we do not know the origin of the substrate and/or decorative elements, we can check their pH with a vinegar test. We pour vinegar over our elements. If there is a reaction (bubble) our equipment is alkaline and we should be cautious if introducing them as aquarium decoration and monitoring the water quality regularly is highly advised.


The occurrence of alkalosis disease is a great example of how important the water parameters are. To put it simply, the disease occurs when the fish live in hard and alkaline water instead of acidic and soft water. That’s why we recommend using decorations made of limestone only in case of setting up a biotope aquarium, e.g. Malawi. Cichlids living in this lake are used to higher pH because limestone is part of their natural habitat.

The conclusion is: control the water parameters, monitor your inhabitant’s behaviour and we are sure that this will be beneficial for your fish health!

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