Diseases, Parasites and other Maladies


This section will discuss ailments that affect the fish kept in our aquariums. I will simply not call them diseases because most are not true diseases but a response to some sort of stimuli such as poor tank water management or the presence of actual parasites. I will list the most common ailments, the reasons behind them and the appropriate action needed to "fix" the problem.



If you maintain good water quality, keep the right kind of fish together, feed good quality food and monitor all your water properties you will rarely have any problems. A few common sense precautions when you purchase new fish can save you a lot of trouble.

A few things to observe:

  1. Are the fish active?
  2. Are they eating?
  3. Are there any scars, spots or open wounds?
  4. Are the gills nice and pink?
  5. Are the fins wide open, not clamped close to the body?

All of these and more should be closely looked at before you buy any fish and never buy a fish that does not look or act right and "cure" it at home! One last important thing, check out the stores filtration system. If the system is a central one be sure to check out all the tanks for signs of parasites as many are free swimming at some point in their lives, and they could move freely from tank to tank.

Once you decide to purchase the fish a few more precautions should be taken in order to keep risk at a minimum.

  1. Slowly acclimate the fish to your tank water.
  2. Use an antibiotic dip if you can.
  3. Ideally have a quarantine tank set up.
  4. Isolate the fish for two weeks in the quarantine tank.
  5. Keep a close eye on the fish once it's in your tank.
  6. Prevention is better than intervention.


These are basic common sense guidelines that can save you fish, plants and money if properly followed. If you find yourself confronted with one of these ailments or some other not described here, please click on the button below for a comprehensive guide to some of the most popular medications available for our use.







Ammonia Poisoning

If too much organic waste is present and the load becomes to much for the bacteria to handle the ammonia concentration in the tank will rise. If the pH is above seven ammonium turns into deadly ammonia and poisoning takes place.
The gills of the fish turn a lilac color and they hang sluggishly just below the water surface panting.
Find the cause of the organic waste and remove, do a large water change and slowly bring the the pH down below seven if required.

Carbon Dioxide Poisoning

Too much CO2 fertilization.
Apathy, restless swimming and panting.
Strong aeration, water change and never fertilize with co2 at night.

Nitrite / Nitrate Poisoning.

Heavy organic load or pollution and not doing enough water changes. Also check water supply, some are high in Nitrates to begin with.
Colors of the fish become more intense or really bright, panting, and hanging just below the water surface.
Find cause of organic pollution and change water to bring down levels.

Poisoning from Tap Water

Tap water varies from area to area and may contain Chlorine, Copper, fertilizer and other pollutants.
Test the water before using and filter with something like the Tap Water Purifier or use water run through an reverse osmosis filter.



Gas bubble disease

Gas Bubble Disease is caused by a sudden dramatic change in gas pressure in the aquarium. This can happen by changing too much water at one time or by adding cold water to the fish tank. Gas bubbles form in the fins and skin of the fish. The bubbles look like blisters and are very easy to see. The skin will crackle if you run your finger across it. If not treated in time, gas bubbles in the bloodstream will kill the fish. The treatment is to add alot of aeration to the aquarium. Lights should be left off to minimize stress. If you see alot of bubbles that have already popped, consider adding a general antibiotic to guard against secondary infection
click for close ups


Bacterial Fin Rot

Bacteria, usually only present in poor environmental conditions.
Frayed fins. Often shortened, with or without a white rim around them.
Any good antibiotic available through the pet shop, check for water conditions.
fin tail-rot


Fish is bloated with scales standing out edgewise.
Causes Kidney damage, treat with a medication for internal infections.


Hexamita or hole in the head disease
Parasitic, Hexamita is a single cell parasite that most often infects Discus, Oscars, Angelfish and The Gouramies.
Loss of appetite, uneven swimming, colors become more intense and pin sized or larger holes appear in the head region.
Depends on the stage of the disease, early stages with only small holes can be helped with the addition of vitamins. Later stages can try a commercially available treatment. It is usually fatal.


Gill and skin Flukes.

Protruding gill covers, with violent and frequent swallowing motions, panting and scratching.
Formmalin bath outside of aquarium, or commercially available cure from pet shop, use caution in aquaria containing invertebrates. Use a secondary antibiotic to help with healing.




Ichthyophtirius or ICK

Parasitic, probably the most common affliction seen by hobbyist.
Small white pustulates that look like grains of salt covering the body and fins. The spots are uniform in size. The fish will "scratch" on anything and breathe rapidly. ICK is light sensitive and can be easily seen when your light is first turned on.
Although very common it can be cured quite easily if caught early. The most common medication is Malachite Green. Malachite Green is mistakenly thought to be copper based, but this is not true. To read an article explaining this please click here "Malachite Green". It will be toxic to any invertebrates. There are many brands available.
click for pictures and more.




Parasitic. Single cell parasite that attacks around open wounds and then spreads to the gills.
Yellow brown or gray looking dusting on the body area. Most noticeably around the Dorsal fin area. Fish are panting and scratching.
Any commercially available medication.


Unknown, but possibly fish tuberculosis, bacterial infection or even over saturation of dissolved oxygen.
Eye or Eyes protrude from their sockets.
Difficult due to its unknown cause, general antibiotic.


Hemmorahagic Septicemia

Bacterial, common in the Live-bearers and Goldfish.
Blood-Red streaks on the fins close to the body, without any signs of skin damage.
Any of the antibiotic treatments, like Tetracycline. Available by many brand names.



Helpful Hints About Medicating and Medicines

It is better to medicate fish in a separate tank with a bare bottom. Treating an entire aquarium can affect the biological bed and result in high ammonia and nitrite levels. Many medications will kill live plants and invertebrates, discolor silicone or be absorbed into the substrate making it very difficult to remove from the the system.

Always follow the manufacturers directions. Using too low of a dose will not be effective and too high of a dose can cause respiratory and other problems. Be sure to repeat the treatments if the directions call for it.

Never mix medications in the same tank unless the directions say its okay to do so.

Remove carbon, resins and all absobative filter media, turn off protein skimmers, ozonizers and U.V. sterilizers. These materials will remove the medication before it has a chance to work.

If nothing cures your fish it may be better to "put it out of its misery" do this as quickly and painlessly as possible by severing the spinal cord behind the head with a sharp knife or scissors. Large fish should be stunned first with a hard blow to the head. (Sorry for this, but sometimes it is needed )





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