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    Common medication used in Aquariums

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    Common medication used in Aquariums

    med2.jpg.bd139dad398a8c57cd5ab45e0d4d317e.jpgComprehending the active ingredients of medication can be as important as understanding what the medication treats. Here is a list a few of the more common medication that is found in Aquarium medication.

    It is probably also important to remember that friendly nitrifying bacteria aka nitrifiers, aka beneficial bacteria can also be impacted by medication. Therefore, knowing what each active ingredient does is all the more important to avoid killing off the friendly bacteria.

    On the other spectrum, we have the unfriendly bacteria which are pathogenic causing bacteria.

    Pathogenic bacteria are opportunistic, as long as the fish is healthy the symptoms are not perceptible. Small amounts of bacteria are always present and a healthy, stress free fish or shrimp’s immune system is able to cope with battling these harmful bacteria. It is when stressed (heat, ammonia, nitrite, high organics, low dissolved oxygen etc.) or through injury that the bacteria numbers multiply and overwhelm the bodies immunity system that we start seeing signs of disease.

    This article will also cover non bacterial medications and medication used for parasites.

    Hopefully the next time you pick up a bottle of medication for your pet, you will know exactly what the active ingredients do and how to apply it to use in your particular situation.


    Antibiotics vs Antibacterial

    There are two terms when dealing with medication that needs to be clarified.

    Antibiotics are naturally produced by another organism, be it plant or animal or microorganism, that kills the pathogenic bacteria.

    Antibacterial substances are manufactured artificially to combat pathogens.

    We will use the term Antibiotic going forward in this article to refer to both terms.

     Which antibiotic to be used for a pathogen is determined by the pathogen’s cell wall. Pathogens have either a thin or a thick cell wall. The method of determining the main types of bacteria cell wall is a technique called Gram Staining. Where dye is used to stain the bacteria.

    A blue-purple colour indicates a thick cell wall and is called “gram positive”, while a pink-red colour indicates a thin cell wall and is referred to as “gram negative”.

     Gram Positive antibiotics prevent the development and repair of the cell wall which eventually will lead to the cell content leaching out, consequently killing the bacteria.

    Gram Negative antibiotics attack by interfering with the protein synthesis (metabolic process) therefore preventing the bacteria from multiplying and growing. Of the two types, Gram Negative is a lot more common in aquatic diseases.

    Using the correct medication is important for the pathogen, as Gram positive antibiotics will not have any effect on gram negative bacteria and vice versa.

    Keep in mind that beneficial bacteria in our aquarium that does the nitrifying are Gram Negative. Some antibiotics may also kill off beneficial bacteria, especially the gram negative medication. Using a Hospital tank for treating sick fish or shrimp is always a good idea. Separating the patient into a smaller tank has many benefits like reducing the required medication dose, reducing the impact of medication on healthy livestock (remember that sentence above about reducing stress), eliminating the risk of harming beneficial bacteria, being able to observe the progress of the treatment without trying to find the sick patient – who will often be hiding.

    Refer to the article on Hospital tanks for further details.

    It goes without saying that using the right medication for the disease is essential. It narrows down the treatment time and the types of medication used. This article is not about disease identification. Although we will talk about what diseases these medications will treat. The application, dosage and duration should be strictly followed according to the manufacturers instructions, including any follow up dosages, even if the fish or shrimp looks better after the first treatment. This prevents flair ups again, and reduces the pathogen’s ability to become immune to the antibiotic. The latter is probably more imperative in the long term.

    The common antibiotics used in aquariums


    treats gram positive bacteria. Some aquarists also recommend Erythromycin to treat cyanobacteria blooms but this should be used with caution and the cause of the cyanobacteria still needs to be addressed.

    Useful for Fin and tail rot, infections attributed to kidney disease (often not true kidney infections), pop eye. Neon Tetra disease (faded colour). Black Molly disease. Most gram-positive and some gram negative bacteria and fungus. And it’s this small impact on gram negative bacteria that you should be aware of, which could impact beneficial bacteria. I say could in italics because I have not experienced a tank crash personally IF correct dosages are followed.


    Aminoglycosides sold as KANAMYCIN, NEOMYCIN, and STREPTOMYCIN

    are active against gram negative bacteria and work well in higher pH alkaline water conditions and is therefore also used in brackish or salt water, especially for Vibrio. It is used to treat many sensitive gram–negative and some gram–positive bacteria. Works well combined with Nitrofurazone for flexibacter (columnaris) (Symptoms: Fuzzy, thin, white coating on the body and fins. Looks like a fungus), as Neomycin is not very good at treating columnaris by itself.

     Kanamycin can treat many sensitive gram–negative and some gram–positive bacteria. Works especially well in salt water aquariums. Effective for whirling disease, suspected kidney disease, pop eye and dropsy. Works well combined with Nitrofurazone for flexibacter (columnaris) and Pseudomonas-Open red sores or ulcerations, fin and tail damage, fins and tail are eaten away.

    Kanamycin sulphate appears to prevent bacteria from making their cell walls, so the cells die.

    Neomycin sulfate is also used in aquarium medications as a broad spectrum antibiotic used to treat bacterial infections and wounds. Some Gram-negative bacteria, and gram-positive, and possibly mycobacterium tuberculosis.

    Particularly effective with notoriously resistant bacterial strains like Aeromonas, Pseudomonas and Mycobacteria. Neomycin is an excellent choice when soaked in foods for intestinal diseases. Neomycin is not absorbed by the intestinal tract and is therefore effective in treatment of intestinal diseases. But Neomycin can damage the kidneys as it is nephrotoxic, so this is a poor treatment choice for Dropsy.

    Neomycin is also poor at treating fungal infections.



    known as sulfa or triple sulfa or trisulfa – Active ingredients are Sulfamerazine, Sulfamethazine, Sulfathiazole. Sulfas have antibacterial characteristics inhibiting the growth of bacteria but do not kill them. Sulfa drugs arrest cell growth by inhibiting the synthesis of folic acid, a component required for growth by bacteria. Folic acid is a large molecule and is unable to enter bacterial cells, so the bacteria must synthesize the compound intracellularly. Animal cells are unable to synthesize folic acid and it must be provided in the diet. For this reason sulfa drugs are not toxic to animal cells.

    Sulfas are a broad spectrum antibacterial medication. Fin and tail rot, mouth fungus and collapsed fins, columnaris, and hemorrhagic septicemia. Very useful for damaged fins caused by fin nipping. Can be used in combination with Malachite Green or Acriflavin (do not combine with copper sulfate) to increase effectiveness. Sulfas are more effective in high pH or alkaline environments, so sulfonamide as well as aminoglycosides can be used in marine environments.



    (Furazolidone, furane, nitrofurazone) are also antibacterial but will lose their potency with increasing pH levels. They are therefore preferred freshwater treatments as is the tetracycline group as they can be used in lower pH environments.

    Bactericidal for some gram-positive and many gram-negative bacteria causing disease in fresh water. Often used with pond fish to treat Aeromonas infections, and can be used to treat Columnaris, Vibrio, and Furunculus.  Also effective in controlling flexibacter/columnaris. Furans are good at treating minor skin infections.

    Can be used with Kanamycin for Aeromonas and Vibrio.

    Do NOT use with Invertebrates or Shrimps.

    Note: Nitrofurazone comes in a yellow powder and can temporarily turn the tank water yellow.



    is bacteriostatic, that is, it inhibits bacteria from protein synthesis. It interferes with the production of proteins that the bacteria need to multiply and divide (bacteriostatic). This drug will get less effective in hard waters as it readily binds with calcium and magnesium. Gram-positive and gram-negative bacteria. Best used mixed in with food if your pH is above 8.0, as it will not work in pH above 8.0. Marine ulcer disease, cold water disease, bacterial hemorrhagic septicemia (Symptoms: Red streaks in body and fins, or redness in the body. Open sores or loss of scales) and mouth fungus. 

    OXYTETRACYCLINE products are very similar to Tetracycline. Oxytetracycline is the second of the broad spectrum tetracycline antibiotics to be discovered. Both work to interfere with the production of proteins that the bacteria need to multiply and divide.



    An antibacterial to treat gram negative bacteria, prevents DNA synthesis and can be used in a broad pH spectrum. Particularly useful on resistant strains of Ich. If your normal Ich meds don’t seem to be effective anymore, try this. Works to control Protozoan infestations, sliminess of the skin and Rams disease (whirling disease). Works great for Hexamita when combined with Metronidazole.


    Non Antibiotic Medication


    work best to prevent fungal and bacterial infections on fish eggs before they hatch. It can also be effective against parasites like Ich and protozoans – though not as effective as the other medications mentioned.

    Great when used as a dip for topical treatment of parasites, bacterial, and fungal infections.

    Best used in a hospital tank rather than treating the main tank. Methylene Blue can harm beneficial bacteria, and plants in the main tank. As a result, Methylene blue is used less often to superior products like Malachite green and acriflavin.



    Used for it’s antiseptic properties for treatment and control of external parasites of freshwater and marine fishes. Can also be used to treat fungal infections on fish eggs which include Achlya and Saprolegnia.

    Malachite green is toxic and is not safe for some sensitive fish and invertebrates however. Some research also shows that the toxicity increases in higher pH so medications with Malachite Green should be used with caution in saltwater aquariums.

    Can be used on Ich, Costia, Chilodonella, Ambiphyra, Cryptocaryon, Epistylis, Trichodina, Oodinium.

    Can be combined with Acriflavin or Formalin.



    Well known as a preservative, as can be seen in the jars preserving scientific specimens. For treatment and control of the diseases caused by fungi, protozoan and monogenetic trematodes of freshwater and marine aquarium fishes. Including Ich (Ichthyophthirius). Most formaldehyde-based medications work better as a bath or dip instead of being used to treat the entire system, and any of these medications should never be used with invertebrates. DO NOT USE WITH SHRIMP.

    Formalin depletes oxygen in the water, so aerate the water during treatment.

    Works well combined with Malachite Green.



    An antibiotic used to treat fish tuberculosis (not harmful to humans) cause by Mycobacterium marinum, gram negative bacteria. As can be seem in Discus, Bettas and Gouramis. But thankfully, fish TB is relatively uncommon. The fish is generally unwell for several months and showing signs of lethargy, anorexic. Fin or scale loss and a sunken stomach are also likely signs of fish tuberculosis. Isoniazid works in part by disrupting the formation of the bacteria's cell wall which results in cell death.



    An antiseptic agent for the skin. Used as treatment of mild bacterial and fungal infections on fish such as mouth fungus, fin and tail rot, fungus, saproglenia. Can also be used for skin parasites such as oodinium (velvet), sliminess of skin, and very mild ich.  Acriflavine is generally used for infections based in the slime coat and skin of the fish, not for “larger” parasites like Ich or worms.


    Parasitic Medications

    Most parasitic medications need to be used with care, as they can be harmful to sensitive fish, and will most definitely kill inverts and shrimps.


    Copper has long been used as medication for parasite treatment in aquariums, especially for “Ich”, Oodinium, fungus and protozoan parasites. Sequestered sulfate copper being the active ingredient. Often you see Chelated copper as the active ingredient for some treatments. Chelated meaning “inactivated”, is often used as a safer alternative to sequestered copper.

    Many algaecides also use copper to eradicate algae.

    Removal of sequestered copper is difficult. Only EDTA and water changes can remove it – Carbon will not remove sequestered copper.

    Seachem Cupramine is a very safe chelated formula and is the safest copper for use in the Aquarium, while also being the easiest to remove after treatment.

    Being a heavy metal, Copper is NOT safe for Inverts, Shrimps or marine/reef aquariums.



    Metronidazole is most commonly used as an anti-parasitic medication to treat protozoan and flagellate infections. Used for Hole in the head disease HTH (hexamita), Head & Lateral Line Erosion HLLE, chilodonella, plistophora (parasite disease usually seen in neons and cardinals that causes loss of colour, darting, and eventually death), salt water ich (Cryptocaryon), bloat. Safe for many fish or shrimp that are sensitive to the copper-based alternatives. Most effective mixed with food.



    Fenbendazole is predominantly a dewormer, and is used even in cattle, sheep, birds, reptiles and amphibians. Used as a treatment against internal parasites like roundworms, tapeworms, hookworms, calamus worms. It can also be used to treat planaria and hydra. Fenbendazole is very effective against these parasites.

    It is relatively safe with inverts and shrimps, however, there have been cases where inverts are harmed when using Fenbendazole at dosages safe for fish. In aquariums with inverts and shrimps, start with half the dosage recommended by the manufacturer. Follow up with a second half dose treatment if necessary rather than performing a full dose in one go.



    Aka PP, can be very useful against external parasites, but can go very wrong if used wrongly.

    PP is a deep purple colour when used, that turns progressively yellow-brown as oxidation occurs. PP is used against larger parasites like flukes, lice and anchor worms and can be used to treat the entire aquarium or, preferably, as a dip or bath. PP oxidises with air, and should be stored carefully. It also stains fingers and clothes !! As I found out accidentally.



    Praziquantel is an anthelmintic or de-worming medication. And is particularly good at it. Used for gill and skin flukes, tapeworms, flat worms, anchor worms and Schistosoma (a worm that lives in the blood stream of the fish). Prazi however is not very good for treating pinworms or roundworms at all.

    Prazi is safe for fish, invertebrates, plants or biological filtration and is even used as a dewormer for cats, dogs and even humans. This medication can be used in tank or soak in food. No water change is necessary, but removal of carbon and uv light is advised to maximise the medication’s usefulness.

    Always complete a full course of treatment. Don’t be fooled into thinking that the fish is cured with the first dose of the treatment.



    Piperazine is a drug that belongs to the family of medicines called anthelmintics. These medicines are used in the treatment of worm infections. Where Prazi fails at treating pinworms, roundworms and nematodes - Piperazine is good at treating these type of worms. However, to be effective Piperazine needs to be ingested with food. Piperazine is heat stable, which means you can mix into food that need to be prepared hot, like agar agar.

    Always complete a full course of treatment. Don’t be fooled into thinking that the fish is cured with the first dose of the treatment.



    is another anthelmintic (anti-worm) agent  commonly used in large livestock such as cattle, pigs and sheep – and more recently fish. Levamisole HCL is safe to use in aquaria and effective against many internal parasites, especially nematodes, when used in appropriate dosages. Roundworms, Hookworms, and Nematodes species such as Capillaria, Eustronggylides, Camallanus, and Contracaecum are treated by Levamisole HCL.

    It does not harm the bio-filter, plants, invertebrates or uninfected fish.

    Levamisole HCL is ineffective for Tapeworms, flatworms or flukes. Use Praziquantel for those.

    Levamisole HCL is most effective when absorbed through the gut, which means treating the food you feed the fish. Some medication can be absorbed by the skin from the water as well, and Levamisole HCL is stable enough in the water for up to 90 days to do it’s job. Levamisole affects the neurotransmitters and paralyses the worm (spastic paralysis). The fish then passes the inactive worms. Good gravel vacuuming is advised after treatment to remove the paralysed (but still live) worms.  It is not ovicidal, which means it will not affect eggs already present, but it will affect the larval stage of the worm. To ensure complete eradication of the parasite treat again after remaining eggs have hatched. Treatment in a hospital tank is advised strongly. The hospital tank can be sterilised after treatment thoroughly.

    Levamisole HCL is light sensitive.

    Store product in tightly closed light resistant containers. Leave off tank lights when treating. Levamisole HCL is a safe and effective anthelmintic for use in aquariums. It does not harm the biofilter, plants or invertebrates including shrimp.

    Always complete a full course of treatment. Don’t be fooled into thinking that the fish is cured with the first dose of the treatment.



    Trichlorfon aka Dylox, is usually used in freshwater aquariums or ponds, as it degrades rapidly in high pH, reef aquarium water.

    Primarily used to treat parasites like: Hydra, Lernia (Anchor Worms), Parasitic Copepods, Monodigenetic and Digenetic Flukes, Fish Lice (Argulus), Leeches.

    Trichlorfon is very highly toxic to invertebrates.

    DO NOT USE ON FISH THAT ARE CHEMICALLY SENSITIVE such as: Silver Dollars, Rays, Bala Sharks, Arowanas, Tinfoil Barbs, Hemiodus, Piranha, Most Silver Scaled Fish, Marine sharks, Lion Fish.

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