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Aquarium Medications; Anti-Parasitic - by Carl Strohmeyer

This article deals with medications generally intended for the treatment of internal and external parasites.

When you have fish that are sick (bacterial, fungal, protozoan, or other parasites), you want to try and isolate them in a hospital aquarium whenever possible. Regular water changes before each treatment allow for a more effective treatment, especially when treated in the display aquarium.
Sponge Filters work well in hospital aquariums. Remember to remove carbon, as carbon will remove many medications. Also note that silicone in the aquarium will absorb malachite green, methylene blue, and copper sulfate. Most corals (crushed and otherwise), and ceramic decorations will also absorb medications such as malachite green, methylene blue, and copper sulfate.
Proper calcium levels are important, as calcium also helps in healing and stress, and without proper calcium levels healing may be difficult or impossible. The addition of antibiotics (such as Tetracycline) will lower calcium absorption.

One more note as to the use of medications to treat aquatic diseases; Make sure all your water parameters are where they should be, if for example your ammonia levels are high, all the medication in the world will not help, in fact they will only exasperate the problem. Make sure you have proper water circulation and even more importantly enough dissolved oxygen and low waste particulates, otherwise your Redox Potential  can be adversely affected (this is not to say Redox Potential needs to be worried about for the average aquarist). Adequate calcium levels (which can be partially measured by kH) is very important to proper osmotic function. For more information here see this article; http://www.americanaquariumproducts.com/AquariumKH.html

If any of the above parameters are out of sorts, you will have trouble affecting a cure, even with proper medication.

And above, proper efficient water changes (with proper electrolytes; salt magnesium, calcium) can do wonders without medication, so use ALL medications sparingly!!

Dimethyl (2,2,2,Trichloro-1-Hydroxyethyl) Phosphonate:

Trichlorfon is an Organophosphate and degrades rapidly (approximately 99% of applied degraded in 2 hours) in alkaline pond water (pH 8.5) at room temperature. But remains stable in the same pond water held under acidic (pH 5.0) conditions for 2 hours.
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, Hemodias, Piranha, Most Silver Scaled Fish, Marine sharks, Lion Fish.
See methylene blue if Dylox treatment is not available or viable

USE: Trichlorfon is useful for treatment of: Hydra, Lernia (Anchor Worms), Parasitic Copepods,  Monodigenetic and Digenetic Flukes, Fish Lice (Argulus), Leeches
CLOUT contains Trichlorfon (Dimethyl (2,2,2,Trichloro-1-Hydroxyethyl) Phosphonate), as well as; 4-[P-(dimethylamino)-O-phenylbenzylidene]-2,  5-cyclohexadien-1-xylidene dimethylammonium chloride, 1,2,dimethyl-5-nitroimidazole

DOSAGE: There is no recommended dosage (other than Freshwater fish acute toxicity= 1.6-180 ppm), refer to manufacturers directions for all products containing Trichlorfon.
Treat again in 14 days to kill new hatchings of Anchor worms.

INTERNAL PARASITE MEDICATIONS; Piperazine, Praziquantel, and Levamisol


USE: Piperazine is an organic compound used as an anti-parasitic in veterinary medicine, primarily for worms. Piperazine works through anthelmintic action (used to expel or destroy parasitic worms in the gastro-intestinal tract). Their mode of action is generally by paralysing parasites, which allows the host body to easily remove or expel the invading organism. This action is mediated by its agonist effects upon the inhibitory GABA (the chief inhibitory neurotransmitter in the vertebrate central nervous system.) receptor. Its selectivity for worms and similar invertebrates is because vertebrates only use GABA in the Central Nervous System and a worms GABA receptor is a different isoform (A protein having the same function and similar [or identical sequence], but the product of a different gene and usually) to the vertebrate's one.

This product should never be used in the presence of invertebrates as for the reasons outlined above. Piperazine aquatic uses are restricted to internal parasite control, especially intestinal worms. Piperazine is proven effective for Capillaria Nematode worms that infest the intestines of Angelfish, Discus, some other cichlids, and occasionally other aquarium species. In the aquarium the disease spreads easily from fish to fish as they consume the eggs of the worms, shed in feces of infected individuals.

Piperazine is found in Prazipro, Pepso Flakes, and the now discontinued Tetra Anti-Parasite Flakes


Praziquantel is an anti-worm, medication. It prevents worms from growing or multiplying in the body. It is used to treat infections caused by worms, especially trematodes, commonly known as flukes and flatworms.

Praziquantel is found in Jungle Internal Parasite Guard and Aquarium Products Gel Tek Medicated Food (which is a better mode of treating with this medication)

Levamisol has a wide range of anti-nematodic effects. It is efficient in destroying both adult and larvae forms of gastrointestinal and pulmonary nematode parasites in fish. It attacks  parasites by causing first paralysis and then death of the parasites. Partly decomposed parasites are being eliminated during the first 24 hours since the beginning of the medicine application.

Levamisole is found primarily in wormers for animals at veterinary supply houses and treated a 5 ppm. This was also found in an Aquatronics product no longer available (a good one at that); Discomed.

DOSAGE: Refer to product instructions containing these medications (Do NOT use any of these in the presence of invertebrates)

METHYLENE BLUE (Zinc Free) 2.303% :
A heterocyclic aromatic chemical compound with molecular formula: C16H18ClN3S.

Methylene Blue is widely used a Redox indicator in  chemistry. Solutions of this substance are blue when in an oxidizing environment, but will turn colorless if exposed to a reducing agent.
Due to reducing agent properties, methylene blue is used as a medication for the treatment of methemoglobinemia. Methemoglobinemia can be caused by high nitrites (and ammonia) in the blood, which happens in fish respiration in water high in ammonia or nitrites. Methemoglobinemia is treated with the use of methylene blue, which restores the hemoglobin to its normal oxygen-carrying state.
Methylene Blue is made from the anti-malarial drug, chloroquine. Malaria is a protozoan similar to the protozoan that causes ich (Ichthyophthirius multifilius) and oodinium, which is why Methylene Blue is useful for parasite and fungal treatments

 Fungus on eggs, Ich, fungus and some bacteria. Effective in gill disease. Transports oxygen. Some protozoa, sliminess of the skin and oodinium. Great for use as a 30 minute dip at double dose.
Very effective when used as a dip for topical treatment of parasites, bacterial, and fungal infections. When Dylox is not available, this can a useful treatment for anchor worm (especially in goldfish); first carefully remove the anchor worm with tweezers, then dip the affected fish in Methylene blue. When used with a UV sterilizer to kill the swimming stage of the female anchor worm (the female is the parasite), this can be an effective treatment. (Tank can also be treated with Malachite green or malachite green combination during this time for improved effectiveness).

 10 gallons every other day for 10 days with water changes before each treatment. BEST USED IN A HOSPITAL TANK. Methylene blue can destroy nitrifying bacteria and plants in the display aquarium.

My preferred use of Methylene Blue  is a bath. To prepare this bath I use 1 teaspoon 2.303% solution per 5 gallons (double dose) in a bath of aquarium water from the tank the fish you wish to treat came from, I usually use about a ½ gallon of water, however you may use less. Measurement of the Methylene Blue does not need to be precise as this bath should be used for about 30 minutes (although do NOT overdose). Make sure you keep the water in a warm area, as in a cold room the water temperature can drop rapidly which would stress the fish. Do NOT pour this water back into your display aquarium when finished. This can be performed twice per day.


USE: For treatment and control of various external parasites of freshwater and marine fishes. When used as directed the medication will control or prevent the following common protozoan parasites:
*Ichthyophthinus (freshwater Ich) exhibited as fine “salt like” white spots that usually first appear on the fins.
*Costia (Ichthyobodo). Not to be confused with ich, is a parasite that can live dormant on healthy fish (primarily their gills), then under certain conditions (poor water conditions, stress, ECT), reproduce rapidly. Symptoms of an outbreak include Heavy and labored “breathing” flashing and rubbing, skin cloudiness caused by excess mucus.
*Chilodonella, *Ambiphyra, *Cryptocaryon (marine Ich), *Epistylis, *Oodinium and Trichodina, *Plistophora (best combined with formalin at 1/2 strength)
Malachite Green is also effective against common external fungal infections of fishes and eggs which include Achlya and Saprolegnia.
DOSAGE: 1 teaspoon of a 0.038% solution per 10 gallons every other day for 10-14 days. Or 1 drop of .50% solution per gallon every other day for 10- 14 days. 25% water changes are recommended before each dose. Use half dose for scale-less and delicate fish such as Clown Loaches and Neon Tetras. Double dose for marine aquariums.
Note; malachite green is more toxic at higher ph.
Can be combined with Formalin or Acriflavin.

Quick Cure is a very effective combination of Malachite Green and Formalin

Another excellent product product with malachite green is: ParaGuard. ParaGuard employs a proprietary, synergistic blend of aldehydes, malachite green and fish protective polymers 

For more information about ich (Ichthyophthinus)

FORMALIN (3% formaldehyde):

USE: For treatment and control of the diseases caused by fungi, protozoan and monogenetic trematodes of freshwater and marine aquarium fishes. Formalin will control or help prevent diseases of fishes caused by the following disease organisms: *Ichthyophthirius (freshwater "ich"), *Costia (Ichthyobodo), *Chilodonella, *Ambiphyra, *Cryptocaryon (marine "ich"), *Epistylis, *Oodinium, *Amyloodinium, and *Trichodina.
DOSAGE: 1 teaspoon of a 3% solution per 10 gallons every other day for 10 days. Combines well with malachite green.
Formalin can deplete oxygen in an aquarium, so consider adding an air stone or a power head with an air diffuser.

Quick Cure is a very effective combination of Malachite Green and Formalin


USE: For treatment freshwater and marine ich, Oodinium, external parasites, fungus and even algae. Very effective when used properly and carefully. One the more effective treatments for freshwater Velvet (Piscinoodinium pillulare), as copper will attack both swimming stage and the dormant stage (as this is when the parasite uses its chloroplasts to produce nutrients, and the copper destroys these).

DOSAGE: Treat according to your solution to bring your copper level to .15 -.20 ppm. Sequestered Copper (often called chelated, but that is incorrect, chelated means inactivated) sulfate works best (citric acid help achieve this). Soluble copper salts work well in freshwater only.
Please not that copper, basically kills the parasite by poisoning it more than the fish, so never overdose.
Do not use with snails and other invertebrates, do not use in reef aquariums, and note; when uses as an algaecide, the copper is absorbed by the algae then released when it dies. Removal of sequestered copper can be difficult, only EDTA (Ethylene Diamine Tetra Acidic Acid) and water changes remove it, NOT carbon.

For an effective treatment for ich, fungus, and especially Velvet, Medicated Wonder Shells are extremely for Velvet in particular as they have three of the most effective ingredients for the treatment of Velvet; Copper Sulfate, Acriflavin, & Methylene Blue. They also add electrolytes and calcium, essential for proper healing.

For my full Aquarium Medications and Treatments article, including expanded information about the above medications and in addition many more different medications used in aquariums, please see this article:




Professional aquarium maintenance experience since 1978 as the owner of one of the larger aquarium maintenance companies in LA, CA.

I have been in the hobby since 1969.



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