Home Problems & Solutions Fish Keep Dying but Water is Fine (The Remedy)

Fish Keep Dying but Water is Fine (The Remedy)

by gvald

The fish in your aquarium won’t stop dying even though you just changed the water? No worries, we have the solution, it can come from many places, so here are the following questions to start with:


How often do fish die in clean water?

How many fish die?

The loss of a fish is not a cause for concern, unless it shows signs of disease, which we will see below. Fish are like us, they can have internal deformities that are totally invisible or die of old age, it is better not to treat the whole aquarium in this case and just wait and monitor the water parameters. The benefits and risks of a possible treatment would not be conclusive


The loss of many fish on the same day

Again, observation is the first thing to do. If the fish show signs of disease, a treatment should be used as soon as possible, but first, the parameters should be checked. In this case, Nitrite, PH, KH, GH and temperature should be monitored, so a prudent aquarist should always keep a drop test kit on hand.


The loss of a fish every 24 to 48 hours

This is the most complex case to solve, it will be necessary to check for the presence of disease and all the parameters available here in case of a negative result, it will be necessary to consider a carbon filtration to eliminate any external pollutant that could have entered the aquarium.


Try to remember what has been done in the aquarium in the previous days (addition of new fish, plants, cleaning etc.) and consider a big water change of about 50%. Do not hesitate to contact us we can help you.


Diseases to check for in case of fish death

Simple bacterial diseases: they are often called rot, fin rot, or oral or exophthalmic when it affects the eye. It presents in the great majority of cases very characteristic signs like frayed fins, flat or raised whitish spots on the body of the fish, deformed and white cottony mouth or exorbated eyes. It is necessary to act quickly because the quantity of bacteria can double every hour and are very contagious.


In this case we advise to treat the whole aquarium unless only one fish is affected or a treatment in a hospital tank is possible. The usual treatment is based on a product called general disinfectant like Tetra Medica FungiStop and able to stop bacterial diseases quickly if taken in time.


Fungal diseases

This type of disease is relatively rare in the aquarium trade and is caused by fungi but is often confused by the aquarist with bacterial diseases.  They can affect any part of the fish’s body. It often appears as a patch or cottony line on the fish.


The disease is often due to poor water quality which attacks the protective mucus of the fish or to an untreated plague. The evolution of the disease is often slow and the survival of the fish will depend on the affected area, the speed of treatment and especially the quality of the water.


Viral diseases

They often affect the internal organs of the fish, they are contagious and the clinical signs can be quite discrete. You should look for discoloration, bulging eyes and swollen abdomen.


Unfortunately there is no treatment against viruses, it will be necessary to isolate the affected fish, add banana leaves or cinnamon bark. We can also add a general disinfectant to prevent bacteria from taking advantage of the weakening of the fish to manifest themselves and keep the hospital aquarium in the dark.


Parasitic diseases

There are several and the symptoms can be very different


The white spot disease: the symptoms are small white spots in relief which appear on the whole body of the fish. they are caused by a small parasite named Ichthyophthirius, the parasite comes to fix itself under the skin of the fish and forms a blister called vulgarly “white spots” the parasite will remain under the skin of the fish a few days the time to develop before going out and to reproduce at the bottom of the aquarium.


As long as the parasite is under the fish’s skin, the treatment will not be able to destroy it. The cycle is more or less rapid depending on the water temperature, which is why it is necessary to increase the temperature so that the treatment can act more quickly. It is essential to treat quickly because this disease can generate a significant mortality especially since it can be treated very well.


Anchor worms

They are worms that attach themselves partially or completely under the skin of the fish. They are often seen through transparency because they are quite large (up to 1 cm), the best way to remove them is to take the fish out on a wet cloth and remove it with tweezers. The fish should then be isolated in a hospital aquarium with an anti-bacterial treatment to prevent bacteria or fungus from developing.


The gill worms

As their name indicates, these are small worms that attach themselves to the gills of the fish. The diagnosis is simple on large fish where lifting the gills is easy but on smaller fish it will be based on behavior. The fish may lack air, be weakened and lose their colors, often rubbing against the decorations in a vain attempt to remove them. In this case, only a treatment of the entire aquarium will be able to get rid of them.


The 2 parameters that can cause the death of fish in clean water

In case the fish do not show any disease as described above, most of the time there are only 2 obvious causes, which are nitrites or an unstable pH:



Nitrites occur when the aerobic bacteria in the filter are not sufficiently numerous to transform the waste into nitrate, either because there is too much waste or because too many useful bacteria have been eliminated by treatment or cleaning.


Nitrite enters the bloodstream of the fish and prevents the red blood cells from transporting oxygen properly, so the fish die from suffocation. When nitrite rises, the fish all rise to the surface in search of oxygen, the water can become milky but the only way to be sure is to perform a drop test for NO2.


An unstable pH

The variations of PH are extremely harmful especially since the scale is particular. The movement of one degree of PH gives a water 10 times more acid or alkaline but with 2 points it is 100 times more acid or alkaline. Imagine what the animals go through when this variation occurs twice a day.


There is no symptom of acidosis except an important mortality, the only way to diagnose it is to check the PH with a drop test before turning on the light in the morning and in the evening before turning off the light if you notice that the PH has moved you will have to do a complete check-up of the parameters.

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