Diseases Caused by Poor Tank Conditions and Mal Nutrition – Part 1

In some cases, the root causes of the diseases in fish are environmental conditions such as nutrient levels, water temperature, stress, etc. For the best and in-time treatment of the diseases, it is important to know the root cause and well diagnosis. In this article, we will see what are these causes, symptoms and how to treat the affected fish.

Note: For the very well-being of fish, it is always better to prevent any disease before it appears. To do this the fish keeper has to know the fish and its requirements before having the fish and condition the tank accordingly.

Ammonia Poisoning


Ammonia poisoning is environmental harm to fish or aquatic life. The root cause for ammonia poisoning is Unionized Ammonia (NH3). It can be fatal for aquarium fish. It often occurs in newly set up tanks. The effects can take days to appear but it happens at once. The worst thing about it is that the increased amount of ammonia is not visible. Even the signs of ammonia poisoning are not that evident and often it is too late until an aquarist understands that ammonia poisoning has struck his aquarium fish. Due to this, it will be best to test the water especially during the setup and cycling stage which is covering 2-3 months from the beginning.


It is one of the most fatal aquarium diseases, therefore it is important to learn its symptoms fully and accurately. Knowing the reasons and factors that lead to ammonia poisoning is essential before you learn the symptoms of the disease.

The symptoms are often misunderstood by the aquarists. But, you can avoid this fatal mistake and save your fish. Just keep on testing the levels of ammonia in the water and when you find it above the normal range, look for the expected symptoms in the fish. And make a water change to reduce the levels.

The first sign of ammonia poisoning in fish is difficulty in oxygen intake. You can observe the fish gasping for oxygen and often swimming close to the surface. The fish becomes lethargic in its movement and loses appetite, too in the following stages. The gills change their color and look as if they are bleeding because of the lilac or red shade that overpowers them.

Sometimes there appear red streaks on the body of the fish as well but this happens when the damage in the body of the fish increases because of ammonia poisoning. In some worse conditions, the fish settle with clamped fins in the bottom of the tank.

If the medication is not given to the fish on time, the damage starts in the internal organs as well. The brain and central nervous system suffer and the fish starts bleeding internally. The bleeding extends to the external body as well and the fish eventually dies. And these happen very fast in most cases before you notice that there is something wrong.


You should be more observant of ammonia poisoning signs when you set up a new tank for your fish. In older tanks, ammonia poisoning can take place if you add too many fish in the tank and overfeed. The crowded community is a well ground for ammonia poisoning. The failure of the filter also causes the level of ammonia to increase. Regular filter maintenance and using a proper size filter with biological media are essential. The use of excessive medicines that kill the bacteria in the water also causes an imbalance in the water which results in ammonia poisoning.

Any decomposing agent in the aquarium can increase the level of ammonia in the water – an aquatic plant that dies and decomposes in the water or a dead fish hidden in the vegetation or stuck behind the little rocks can be an active source of ammonia generation and this leads to poisoning. Another key agent for ammonia increase is the leftover food particles that rot fast and increase bacterial population which then release harmful digestion wastes(ammonia) in the water.

Keep an eye on your fish and aquatic plants. If any one of these dies and decomposes in the water, the whole environment suffers from increased ammonia levels. Feed the fish with an adequate amount of food and scoop out the leftover food particles to keep the environment clean.


When you find that ammonia poisoning has struck your fish tank, the immediate action you take is to lower the pH level of water. This provides the fish with some good relief instantly. After that, make a large water change and keep doing water changes regularly. Several water changes within a short period can assuredly bring down the level of pH. When the ammonia level is lower than 1 ppm, it is proper for the well-being of aquatic life. But as far as the level is above 1 ppm, keep on making water changes. – Regular water changes are necessary for a healthy aquarium. The water changes mentioned in this treatment section are the immediate actions to lower the levels of ammonia in an affected tank. –

Severely distressed fish needs that you use chemicals to bring down the level of ammonia more effectively. Keep the food amount strictly sufficient so that there is no leftover food. If the ammonia level is dangerously high, stop feeding the fish for several days. After discovering the high level of ammonia in the tank, do not add new fish in the tank. When the level of nitrite and ammonia falls around zero, you can add new species.

To bring the tank water at an accurate level for healthy aquatic life, test both the pH level and ammonia level. They both are related and when pH rises above normal level: 7.0, ammonia becomes more toxic.

When ammonia reaches 1 ppm or 1 mg/l in the fish tank, it is dangerous for the fish though they do not show immediate signs of distress. If the fish stays for a prolonged time in the water with high ammonia poisoning but lower than 1 ppm, they suffer badly and the poisoning may be fatal. That is why regular testing and regular water changes are necessary for the health of fish and other aquatic livestock.

There is one important point to remember in ammonia poisoning treatment, your fish can die even after the level of ammonia poisoning starts dropping because you may start the treatment too late and left the fish in ammonia elevated water for too long.

You can also encourage the growth of beneficial bacteria in the aquarium if you establish a good nitrogen cycle. The growth of beneficial bacteria breaks the development of harmful bacteria (creating Nitrogen-based wastes).

For starting the growth of beneficial bacteria in your new aquarium, it is a good option to borrow a cup of gravel from the deeper layer at the bottom of a well cycled and healthy maintaining old setup aquarium. This gravel will be full of anaerobic bacteria which helps to oxidize ammonia into nitrite and then into nitrate (NO3). Spread this gravel on the floor and then cover it with new gravel that you want to spread in your aquarium. This can cycle your aquarium in 3 to 4 weeks rather than 3 to 4 months if you do not seed it with old gravel.

You need to add new fish species gradually into your new tank. Never overcrowd the tank or mix different species that do not match in their social behavior or habits. Feed on fixed times and do not overfeed the fish.

Changing the water regularly and testing the ammonia level is the key to keep your fish stay safe from ammonia poisoning. Keep these prevention methods in focus and your fish will never suffer from fatal ammonia poisoning.

Velvet Disease


Though the name sounds good, the disease in itself is highly contagious and can be fatal in some cases. It is a common disease of aquarium fish and can attack all the fish in a tank. It is also called Gold Dust Disease or Rust. The responsible parasite for this disease is known as Oodinium. These are tiny parasites some of which are categorized as protozoans and some as algae. Oodinium attacks both saltwater and freshwater fish.

Velvet disease is apparent by its velvety, dusty, yellow or gray look on the skin of the fish. The dusty patches on the skin of the fish are a clear sign of the disease and it is easy for you to detect the velvet disease because of these.

Oodinium parasite attacks freshwater fish and Amyloodinium parasite attacks marine fish. The most common suffering fish are tropical fish and to a lower extent marine aquaria. This disease is more dangerous for the offspring of the fish which are fully eliminated when attacked by this parasite.

Once the parasite attaches to the fish, it feeds on the live organic matter through its roots which are used to attach to the fish’s skin. It develops a protective shell inside and then reproduces. The reproduction is through cellular division and when the spores become more than 200, they become dinospores and hatch out to search for new hosts and restart the whole process.


Velvet disease is an infection and the severity of the infection determines the symptoms. In the beginning, when the infection is mild, the symptoms are some behavioral changes in the affected fish. They twitch their fins frequently or rub their bodies against objects in the aquarium.

When the infection develops more, the skin of the fish loses its natural shine and smoothness. It rather looks opaque and dusty because the mucus starts developing excessively on the skin to fight the parasite.

The parasite also damages the gills and the fish faces difficulty in breathing. If the infection is left untreated, it can get severe and the breathing completely fails which will be surely fatal for the fish.

The severe infection creates more symptoms like dull eyes, ulcers on the skin, losing or detaching skin and exophthalmia (abnormal protrusion of the eyeball or eyeballs).


Poorly maintained aquariums are the breeding grounds for the parasites responsible for the velvet disease. The abrupt increase or decrease in the water temperature also encourages the growth of this parasite. The water temperature that is ideal for the aquarium community should be kept stable to save the fish from sudden increase or decrease in the good or bad bacteria of the tank.

Any new fish obtained from fresh natural water resources or a pet shop need to go through the quarantine process before introducing to the main tank. If you add it to the aquarium without the quarantine process it may trigger the growth of the parasite responsible for the velvet disease. The case is the same with the new plants that you buy for your fish tank. First, disinfection is necessary and then you add them to your fish tank.

Old water is a major cause of the rapid growth of the harmful parasite. The best thing to do is to change the water regularly and keep it regularly tested to check if the chemical setup of the water is ideal for your fish.

These causes are clear and if you can successfully prevent them from happening with your fish, you will enjoy healthy and beautiful aquarium life.


As soon as you find traces of velvet disease on your fish, rush for the treatment because the disease is highly contagious. And it reaches advanced stages even before you find symptoms and diagnose that your fish is suffering from velvet disease.

Copper sulfate is ideal for treatment. Follow the directions of the manufacturer and use it for full ten days to eliminate the parasite. Quinacrine hydrochloride (Atabrine) is another alternative for the treatment of velvet disease. Before applying any chemical treatment make sure that you remove the activated carbon from the filter because it removes the medicine from the water.

Oodinium parasite depends on light for growth and reproduction. Reduce the aquarium lights and dim the few left to discourage the infestation during the treatment. You can also increase the salinity of the water and increase the temperature of the aquarium to 28°C to make the treatment process faster. Adding salt helps the fish to breathe easily which becomes labored because of the deteriorating gill tissues.

The most commonly used treatment is using copper sulfate but not all types of fish can tolerate this treatment, build good knowledge about fish tolerance before deciding on the treatment type and chemicals.

Methylene blue or Quinine are other alternatives. You should better check at a fish supply store for the right choice or ask a friend who has a long experience of having the fish tank at home or for the best consult a vet for the treatment.

Prevention is always better than the best treatment. Keep your fish free of stress because stressed fish is an easy victim of parasites and bacteria. Stress can be mostly because of the poor maintenance of the aquarium or too much fish in a little space.



Dropsy is an old term that comes from the Greek word hydrops. Dropsy is a name given to a condition in fish when they suffer from edema. The soft tissues of their bodies swell. The condition is caused by water and other fluids which abnormally gather in a sick fish’s belly. The term is not used for humans but only for fish. It describes the exact look of the condition in which the belly of the fish swells and drops down. It is also called “bloat.”

Dropsy is a common symptom that happens to aquarium fish. It is a symptom and not an actual disease. Some internal problems cause the dropsy disease in fish. If these problems are correctly diagnosed and you treat the fish on time, the swelling heals. Dropsy can strike any fish in the aquarium but goldfish suffer the most. Fish under stress is the most triggering cause of dropsy and the underlying infections.


The most obvious and the first sign of dropsy is the swollen belly of the fish or bloating. The fluids and water accumulate in tissues and body cavities. The central point of the swelling in the belly. But it can happen on other body parts as well like the pinecone where the scales obviously stand out. The anus becomes swollen and the eyes bulge out. The gills become red but pale and dull. Fish passes out stringy feces.

Some behavioral changes also take place like fish become lethargic, stays at the bottom of the tank most of the time. Sometimes it hides behind the aquarium plants or little rocks or just hangs at the surface area. It also loses appetite.

If the fish does not get the right to diagnose on time and you do not know the underlying cause of dropsy, the symptoms progress. All the above symptoms become worse. In that case, the following advanced Symptoms can be observed;

The anemia because of lack of appetite starts showing in the color of the gills. They become more colorless. The swelling of the abdomen increases and the digestive system becomes less functional and also fish cannot exert properly.


As mentioned above, dropsy itself is not a disease but it is a symptom that shows some internal disorder in the body of the fish. There are multiple different causes of dropsy. Often bacteria and parasite attacks cause infections in the fish which lead to dropsy. The causes that contribute to the spread of bacteria or parasite in the environment and become an underlying reason for dropsy are as follows:

Temperature is one important issue. The temperature of the aquarium should ideally be fixed at 24 to 26°C. This temperature helps the fish to have good digestion which is the key to good health. But this is not the only temperature set up that is ideal for your fish. You need to do a little search on the type of fish and its ideal tank temperature. Once you set up the temperature that is suitable for your fish, you save your fish from many health problems.

If your fish is lacking in nutrition or it has stress, be more vigilant to its behavior because it affects negatively the immune system and it can easily be a victim of dropsy and other diseases. Only your close observation and proper care of the fish can enable you to act on time.

Bad water quality is another cause of dropsy. Bacteria grow rapidly in bad water and the chances of multiple sorts of infections in the fish increase accordingly. You need to keep the water clean and according to the requirements of the fish species you have. Cleaning the filter regularly is also necessary to keep it properly working. Use only aquarium cleaning agents and keep the water chemistry balanced for your fish.

Nutrition is very important for keeping the fish healthy. Poor quality of food weakens the immune system of the fish and it becomes an easy victim of infections and diseases. Get the food only from good brands or stores if you are getting frozen or packed food. Make a blend of fresh and dry food for your fish. A shelled pea per fish twice a day supplies some necessary nutrition. Keeping the feeding routine is also important. Try to feed the fish with a proper amount of food and regular times of the day. Do not overfeed as well as do not feed them less than they need. Feeding the fish twice a day with the correct amount is the best way to keep them in good condition and health.

Another cause of dropsy in fish is an uncomfortable social situation. Some fish fight with others and bully them. The victim remains under stress and suffers from physical injuries as well as uncomfortable. This enhances the possibilities of infections – the underlying cause of dropsy.

Other causes of dropsy can be shifting to another tank where the water chemistry and environment are new to the fish and unsuitable.


Like any other ailment, treatment of dropsy is also best and easy to treat when the disease is still in its initial stages. Before the symptoms become worse, starting the treatment to ensure timely healing and longer life of the fish. The first sign that you observe is the behavioral changes. Just gain the habit of observing your fish closely every day and you may easily notice the changes in behavior. The fish can stop eating food and keeps away from any social contact, hides away in the plants or at the sides of other objects. Two to three days after the loss of appetite will follow and the belly starts swelling. The second day is the ideal time to start the treatment to have a better chance to succeed.

Quarantine is the first step in treating dropsy. Dropsy is not contagious but the infections that are the underlying causes are the most contagious. Quarantine ensures preventing the infection to transfer to one another.

Salt Treatment solves many health issues in fish. Add 1 teaspoon of salt for every 4 liters of water in the treatment tank. Change the water regularly and add salt to the freshwater but adhere to 1 teaspoon per gallon of water. Also using Epsom salt in combination with the sea salt (no iodine) can provide the best results.

Feeding your fish healthy food is the key to a good immune system which gives the fish a strong defense against infections and diseases. So, of course, don’t forget to start feeding the fish high-quality food. Again, shelled peas would be the best option here to help digestion.

The use of antibiotics specific to aquarium fish can be also helpful. But before using any, ask your vet regarding the number of combinations of antibiotics that should be used. Note that there are medications specifically designed for aquarium use so if you find those, just follow the instructions provided.

Observe other fish in the original tank. It is good to perform a clean sweep in the healthy tank also to make sure that no other fish will have the problem, especially if they are not showing any symptoms yet.



Hexamita is a disease that attacks fish caused by protozoa that are classified as intestinal flagellate. It gets attached to the intestines of the fish and causes infection in the digestive system. Only certain types of fish species mostly suffer from Hexamita which are Cichlids species including Oscars and Discus. Hexamita should not be confused with “Hole in the Head” disease which erodes the head and lateral line and is often called Head and Lateral Line Erosion (HLLE). Mostly, while the fish suffer from these two infections at the same time it confuses the people about the real infection.

The intestinal flagellate or the cause of Hexamita naturally exists in the guts of the fish without any problem. But it becomes a cause of infection once the fish is under stress and its immune system has gone weak. The number of parasites increases and it leaves the guts of the fish and passes into the bloodstream. Each protozoa intestinal flagellate can reproduce after 24 hours of its birth and the disease can develop and spread quite fast.


The initial sign is a change in the feces of fish. If they are pale or white in color and stringy, your fish is in the initial stages of Hexamita. The overall look of the fish would be healthy which can be deceiving. Its appetite would be normal but soon other symptoms start appearing. The fish color would become darker. Sometimes it would turn fully black. The look of the head becomes thinner or smaller. The swimming awkwardly changes as the fish start swimming backward. At the advanced stage of the infection, the fish swims with its head pointing downwards. In this stage the nutrition is almost totally taken by the protozoa which are attached to the intestine of the fish and fish gets none or little nutrition from the food it intakes.

Some more advancement in the infection means fish losing weight, looking pale, weak and lethargic. Fish mostly hide in the corners and do not like to move around and be playful. The most significant thing about Hexamita is that even while not moving or hiding, the head of the fish stays facing the bottom.


As mentioned above, the intestinal flagellate lives with the fish without causing any harm. The key factors which cause the parasite to go out of control are poor diet and the weak immune system of the fish. The increased number of the parasite reaches the upper intestine and swims with the intestinal fluids freely and get into the bloodstream. So, if the fish is eating unhealthy or insufficiently nutritious food, it can become a victim of Hexamita soon.

Also, overcrowding of fish in small spaces encourages Hexamita. Transferring fish from one environment to another without taking proper care like quarantine or fixing water chemistry can also cause Hexamita. Fish fighting with one another makes the smaller and weaker fish suffer from injuries and ailments which later lead to a drop in the immunes system.


The best way to treat this internal infection in fish is to add the medicine into its food because the infection is in its intestines and the medicines should directly reach there with the digestion.
Metronidazole is the most popular medicine for Hexamita. You can mix it in tank water where it will be absorbed by the fish and helps to fight the infection. You need to add 100 mg of Metronidazole in 40 liters or 40 liters of water. Every two days make a 50% water change and repeat the process until the symptoms of Hexamita disappear. Often after three times of treatments, the symptoms will disappear. But remember to remove the chemical filtering media in the filters during the treatment like active carbon media.

You can also mix the medicine in the food of the fish. Mix 100 mg of Metronidazole in 1 spoonful of a dried or frozen food or 25g food for one 250mg metronidazole tablet. Put a little amount of water to cover the food and make it moist. Feed the fish with medicated food until the symptoms fully disappear.

  • You can visit our other fish disease and health articles from here.

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