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Medication for Fish Diseases

Updated: Apr 24, 2020

Fish diseases can be a stressful time for both pet and owner as they can quickly overwhelm tank occupants. This is because many fish diseases and infections typically occur in already weakened fish. Fish become weaker and more susceptible to diseases because of bad water quality, low filtration, low oxygen or high algae content. Luckily there is medication we can give to fish and steps we can take to help give them the best chances of recovery.

Common Diseases

Let’s have a look at some diseases and infections first so you know how to decipher what’s going on with your aquatic buddy. The first is anchor worms.

Anchor Worms

These are introduced into new aquariums by infected fish, typically from the pet store. Young anchor worms are very small crustaceans that burrow into your fish’s skin. They enter the muscles where they then begin to develop and release eggs before dying off. The eggs hatch, the new anchor worms need to eat to grow, so they eat your fish from the inside out. This either causes lots of damage which then becomes infected, leading to death, or they simply overpower the fish completely, also leading to death. They can be stopped though!

What to look out for is if your fish is scratching against objects repeatedly while they try to remove the worms themselves. Another indication is simply being able to see the worms, they’ll look like white/light green threads that are coming from your fish’s skin. You might notice inflamed areas with a central point on the fish’s skin too - where worms have already laid their eggs then died off and left the body.

The main method of treating these worms is by physically removing the parasites yourself and cleaning the wounds with an antiseptic, such as iodine. If the worms don’t come off very easily then instead try bathing your freshwater fish in a seawater bath (around 35ppt) for 5 minutes a day, each day until the parasite falls off.

Related Article: Identifying Illness in Fish

Body Flukes

Next up is body flukes, these are flatworms that are only around 1mm long, so spotting the actual worms here is pretty hard. Instead, keep your eye out for other physical signs that may be a symptom. For example, fish with body flukes will try to scratch against objects in the tank in the same way they will with anchor worms but obviously you won’t be able to spot the worms. Another tip is checking if there’s a layer of mucus covering the gills or the body, or if the gills are moving rapidly. Finally, another sign of body flukes in gills or fins that have been chewed on, or reddened skin around them. Pale fish with drooping fins, rapid respiration and/or hollow bellies indicate more extensive infestation.

They’re caused by undesirable environmental conditions including poor water quality, overcrowding and/or stress by incompatible species. These situations create conditions that can lead to destructive outbreaks. Flukes are often present in aquariums but remain harmless under ideal conditions. So keeping on top of your aquarium maintenance and avoiding stressful conditions is a key to prevention, but once an outbreak occurs, prompt treatment is critical. We’ll get into treatment a little later.

Clamped Fin

This one’s fairly easy to spot, the fins will be folded against the body instead of being fanned out as they usually are. This one’s trickier because it's not indicative of any specific illness or disease, it can be a reflection of various problems including parasites or bad water quality. It’s important to first determine the cause and then you can work out a solution. Start by cleaning the tank and boosting the water quality, if it persists then it’[s likely a parasite problem.


Dropsy is caused by a bacterial infection of the kidneys. It causes fluid accumulation or renal failure but it appears to create problems only in weakened fish, this suggests it may come from unfavourable aquarium water conditions. You can pick up on dropsy by noticing any bloating in your fish or protruding scales on their bodies.

Fisk Ick

Fish ick is caused by rapid temperature and/or pH fluctuations and creates spots on the fish’s skin which resembles sand or grains of salt. This skin is irritated so the fish may be brushing up against ornaments in the tank in an attempt to scratch their itch. They may also have clamped fins that are tucked in against the body rather than being fanned out as they usually are and the fish may be gasping at the water's surface.

Fish Fungus

Fungus can be spotted as a gray or white growth in and on the skin or fins of your fish. Untreated fungus appears as a sort of cottony growth and eventually, this fungus continues to eat your fish’s body in order to grow and your fish will die from it. Fish that tend to develop fungus issues are usually already weak or vulnerable. This may be the result of another illness or health issues such as parasites or a physical injury or infection.

Gill Flukes

Gill flukes, like body flukes, are flatworms which are too small to see. Instead, keep your eye out for infected gills and skin and keep a close eye on them, as once their gills are too far gone, they’ll suffocate and die. It’s caused by bad environmental conditions such as poor water quality, overcrowding and/or stress by incompatible species. These environmental factors create conditions that can lead to destructive outbreaks. Flukes are often present in aquariums but remain harmless under ideal conditions. Avoiding stressful conditions is a key to prevention, but once an outbreak occurs, prompt treatment is critical.

Gill Mites

Gill mites are brought into the tank by fish that are already infected, they then spread to the other fish. Mites are absolutely tiny but you may see them if you have a magnifying glass. You’ll notice them around the gill covers and your fish will most likely be gasping for air at the water's surface. The mites stay on the fish’s gills, and attack the fish by feeding on blood and living flesh.

Hemorrhagic Septicemia

For Hemorrhagic Septicemia a variety of different symptoms may occur, though some fish exhibit no external symptoms. Symptoms include hemorrhaging of internal organs, skin and muscle, bulging eyes and bloated abdomens, a general bruised appearance with reddish tints to eyes, skin, gills and fins, open sores or simply abnormal behavior.

The cause of this is an infection that is brought into aquariums by fish already infected with a deadly virus called Viral hemorrhagic septicemia virus (VHSV or VHSv). Unfortunately there is no known cure for this virus.


Symptoms of lice in fish include an aggravated or restless mood. They may also rub up against objects and aquarium glass in an attempt to remove the lice. You may be able to spot them as they look like tiny pale crabs. They appear as flat, dark oval dots crawling on your fish. They feed on the host by using suckers to attach to the fish then pierce the skin.

Usually a lice infestation comes from fish that were living in an outdoor pond at one time and bringing them into an indoor aquarium. Also, fish lice can be introduced from wild fish that are added to an aquarium. Lice travel from one host fish to another, spreading bacteria and viruses, so once they’re in your aquarium, you must get rid of them.

Ragged Tail/Tail, Fin and Mouth Rot

Ragged tail fin or “tail, fin and mouth rot” is the progressive deterioration of the tail and the fins. Fins will become frayed and their colour will fade. It’s caused by a bacterial infection in susceptible fish which are typically those who are bullied by other fish or have been injured by fin nipping tank mates, especially when water quality is poor.

Finally Let’s have a look at was to fix these diseases.

Step one should always be to conduct at least a 20% water change and check what the issues with the water may be. By conducting the water change whether you’ve got unsafe levels of chemicals, too much algae, not enough oxygen or a range of other issues, by diluting the original water you’re also giving a little more time to your fish and yourself while you work out what’s gone wrong. Test the water, we suggest using a Five in One test kit. Once you know what’s wrong, try to fix it first. Whether that’s another water change or it’s adding chemicals, we want the tank water ready because the medicine has to stay in the water, so it’s best to do the water changes before the medicine so that you aren’t removing the medicine before it all gets to the fish.

API also create the Master Test Kit, which is better value than the test strips but take a few minutes longer. Their kit is rated to last for 400 tests!

Next, identify what’s wrong with our fish. Use our explanations above to see if its any of these common diseases. If so then we’ve got good news, medicines are usually very helpful unless your fish has Septicemia, but survival rates for septicemia are shown to be slightly higher with fresh water and medical efforts. The first medicine we recommend is Tetra Lifeguard.

Tetra Lifeguard will work against almost all health issues raised above. Simple drop 1 tablet into the water for every 5 gallons of water in the tank each day for 5 days. Always read the back of the bottle, as some instances require a stronger dose. We recommend having a bottle of Tetra Lifeguard in your cleaning cupboard next to your water treatment and testing kits so that it’s there and on hand if you ever need it.

The next product is another tetra product. Tetra fungus guard helps fight bacterial infections and, obviously, funguses. This comes in very handy for secondary infections, particularly with the health issues that result in your fish rubbing up against things and having open wounds from worms and mites. On the topic of mites and worms, there’s also Tetra Parasite guard. We’re less travelled with this product, however we trust Tetra as a brand and from our experience, their products are reliable and high quality, therefore we’re willing to mention the Parasite Guard.

Another product is from All Pond Solutions. “Aquarium Rescue Parasite & White Spot Control”, while a lengthy title, is a powerful fish tank water treatment that safely disinfects and removes aquatic parasites from your aquarium water. This powerful and fast-acting solution is able to treat most cases with just one application. Aquarium Rescue Parasite and White Spot Control is suitable for use on tropical, marine and ornamental cold water fish tanks

Lastly, we’ve got WaterLife’s product that improves water quality. “Waterlife StayClear A” is a flocculent aquarium water treatment. This means that the particles responsible for causing unclear water will clump together. These larger, combined particles will sink, rather than stay suspended, and will be picked up by your fish tank’s filtration system, leaving your fish tank clear and healthy. StayClear A 100ml treats up to 1000L and is safe for all aquarium livestock and plants. This substance will not cause damage to any filtration system and is suitable for tropical freshwater & coldwater aquaria.

Another Great option is API's Range of products. The General Cure for Parasites comes in boxes of 10 doses and works for both Freshwater and Saltwater tanks! They also offer Fungus cure for any fungal ailments and an option for bacterial infections so whichever issue you're having, API have something for it!

API 5 in 1 Water Test Kit (View Here)

Tetra Life Guard (View Here)

Tetra Fungus Guard (View Here)

All Pond Solutions Parasite and White Spot Control (View Here)

Waterlife StayClear A (View Here)

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