Fish diseases and treatment online guide

Aquarium Fish Disease Treatments and Prevention Guide

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If you want your fish to live long and healthy lives, then you need to make sure that they remain as disease free as possible. Many factors, including stress, bacteria, fungus, parasites, chemicals, and poor water conditions, can cause aquarium fish disease. By monitoring your water conditions daily and checking your fish for signs of disease, you can stay ahead of the game and keep your aquatic pets in prime condition.

  • Spotting problems ahead of time
  • Treating common diseases
  • Preventing disease
  • Using quarantine and hospital tanks

Prevent Aquarium Fish Disease -Actionable Steps

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prevent fish disease
Aquarium fish disease - Treatment and Prevention

Preventing disease is generally the best way to battle physical problems. Sounds simple doesn’t it? It is. You can provide optimal living conditions for your tropical fish simply by following a few simple maintenance routines.

Keeping abreast of the water and equipment conditions in your aquarium, which takes only a few moments a day, gives you a safety margin to quickly correct any problems that show up.

The schedule suggested here gives you a few pointers on watching for signs of disease and other problems such as equipment malfunction.

Daily measure

Maintaining the following daily routine is not as difficult as it sounds. It takes only a few minutes a day, and after a week or so, it will become second nature, just like grabbing a midnight snack while your spouse is asleep.

Check the equipment

It is very important to make sure that all mechanical equipment is functioning properly each and every day. Are the filter systems putting out the optimal flow that the manufacturer suggests? Is the water flowing smoothly, or is it running too slow?

If the water seems to have slowed down to the point where it resembles a still life painting, check to see whether the filter and tubes are clogged and make sure that the motor is not wearing down (water flow is slow or the filter is making noise).

Are the air pumps in your aquarium in prime working condition? Carefully inspect them to make sure that they are running properly and not overheating.

If the pumps are not putting out enough air to run the extra equipment and decorations efficiently (you’ll know when the little plastic diver turns blue and keels over), you can usually rebuild them by replacing worn diaphragms with parts you special order at your local fish shop.

If your local dealer cannot find the parts for you, take a couple of aspirin, then call the manufacturer or check out its Web site to find the parts you need. If the pump is very old and no parts are available, it’s probably time to purchase a new one.

Check the water temperature

Monitoring water temperature is another important part of your daily routine. Any fluctuation in temperature more than two degrees from the norm can quickly lead to serious health problems.

If the temperature is not within correct range (your fish are either floating around in the center of an ice cube or have melted into a blob), check to make sure that your heater is not stuck in the on or off position.

One common cause of overheated aquarium water is excess natural or artificial lighting. Check the amount of natural sunlight the tank receives every day.

If too much natural light is causing the temperature to rise during peak sunlight hours, then you need to move the tank, block out the light with a thicker or darker background, or cover the windows with heavy drapes or shades

The duration and intensity of artificial lighting can be a problem as well. If a light is constantly overheating your tank, switch to a lower wattage bulb or leave the light off longer. Otherwise, your pets may end up looking like floating fish sticks.

Check the fish

After you get up in the morning and choke down a few dozen cups of coffee, make a quick inventory of all the fish in your aquarium. If any fish are dead, remove them from the tank and take them to the bathroom for the final flush.

If any fish seem to be sick or diseased, immediately transfer them to your hospital tank (we explain setting up a hospital tank at the end of this article) and begin treatment. If you check the health of your fish daily, you can take care of problems before they get out of control.

Check the overall health of your fish very carefully. Take a close look at their physical condition. Are they swimming normally, or consistently lurking in the corners of the tank? Are their eyes bright and alert, or clouded over? Are their fins erect, or clamped shut and drooping?

Do they have a straight spine, or do they look like Quasimodo? Do their bodies have normal, well-rounded proportions, or are their stomachs swollen or sunken? If you can visually identify physical problems, you need to check the aquarium’s water and equipment.

Weekly measures

Weekly routines are just like daily maintenance. Choose one day per week to carry out the following tasks.

Check the water

Change at least 15 percent of the water in your aquariums every week. Many large new filter systems and chemicals claim that you never need to change any water ever again if you purchase and use that product. Nevertheless, water changes are a good way to keep the water stable.

The water in a fish’s natural environment is constantly replaced by seasonal rains, tidal flow, and run-off. But in aquariums, the same water remains in the tank between water changes.

Take a moment and pretend that the water in your aquarium is your only drinking supply for the entire day. Would you be comfortable drinking it? Remember, your aquatic pets have to live in it 24 hours a day.

Carefully check your pH and nitrate levels with a test kit each week to make sure that they remain within the range required by your species of fish.

If they are not correct, you can slowly change your pH by water changes or chemicals if your tap pH does not match your species (pH should be kept within 2.0 of the required pH).

If chemical tests indicate that your nitrate levels are too high, the best way to fix the problem is to change 20 percent of the water daily until the nitrate levels return to normal.

Don’t forget to check your aquarium conditions, so that you can identify and correct whatever is causing your nitrate levels to soar higher than the national debt. A few causes of high nitrates include poor filtration, overcrowding, lack of water changes, and chronic overfeeding.

While you are doing your weekly maintenance routine, take time to siphon off any accumulated debris on the substrate’s surface area by using a simple gravel cleaner or aquarium vacuum (see Aquarium Equipment).

Remove any dead vegetation such as decaying plant leaves from the tank. This type of living debris can quickly cause a large fluctuation in the water’s nitrate levels.

If you need to use searchlights to locate the gravel in your tank, then the water needs to be cleaned

Make the fish fast

Ideally, your aquatic pets should fast (that is, not be given any food for 24 hours) at least one day per week. We know this may seem difficult and harsh at first, but avoid the temptation to give them treats such as cinnamon rolls and donuts because you feel sorry for them.

Fasting often happens in the wild and it helps clean out your fish’s digestive systems and guards against constipation problems. Remember to fast your fish on the same day each week, so they don’t go too long between feedings.

Give medications

Take a close look at all the medications you use for common illnesses such as ich and fungus and make sure you have all the standard treatments.

Is there enough dechlorinator (which removes chlorine from your tap water) in your home to make daily water changes if they become necessary? Have you sterilized your hospital tank since its last use? Is it ready?

Being prepared can make all the difference between saving your aquarium fish and losing them.

Monthly measures

Monthly chores are much easier to remember if you mark them down on a calendar. Or you can simply tack a reminder note up on the fridge. Replace all filter mediums that contain carbon. Carbon loses its effectiveness after a period of time.

If your filter isn’t carbon-based, gently rinse it under water to remove debris. Don’t use hot water for this task, as excessive heat can destroy the entire beneficial bacteria colony living on the filter.

Clean all algae from the glass so that your fish won’t think they’ve gone blind.

Common Fish Diseases and Cures

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Fish Diseases and Cures

The list of common aquarium fish diseases in this section gives you general guidelines for identifying and treating various diseases.

Keep in mind that several common medications and salt treatments may be detrimental to live plants, some species of catfish, and other delicate or sensitive tropical fish.

It is always best to treat sick fish in a hospital tank, away from the main population.

Common bacteria infection

Symptoms: Blood spots; open sores; ulcers; frayed fins.

Cause: Aeromonas.

Treatment: Antibiotics.


Symptoms: Reduced appetite; little or no feces; swollen stomach; inactivity. (If your fish haven’t left the gravel for over a month, they may be constipated.)

Cause: Incorrect nutrition; overfeeding.

Treatment: Add 1 teaspoon of magnesium sulfate for every 2 gallons of water. Fast your constipated fish for several days. Improve your fish’s diet by feeding live foods frequently.


Symptoms: Swollen body; protruding scales; fish looks like a pincushion.

Cause: Organ failure from cancer and old age, or poor water conditions.

Treatment: Antibacterial given through medicated food. Improvement of water quality through water changes also provides a little relief to afflicted fish. Complete recovery from dropsy is rare.

Fin rot

Symptoms: Reddened or inflamed rays; torn, choppy, ragged, or disintegrated
fins. Your fish may look like it just swam through an electrical fan.

Cause: Fin rot is a highly contagious bacterial infection that, in its advanced stages, can completely erode the fins and tail all the way down to the body. Bad water quality and fin injuries are usually the main causes of this disease. Fin rot is frequently followed up with a secondary fungal infection.

Treatment: Spot treat infected areas with gentian violet and use proprietary medication (a treatment that is labled for one particular disease, such as fungus cure, ich cure, and so on). Add 1 tablespoon of aquarium or marine salt for each 5 gallons of water. Remove activated carbon from all filters during the medication period. Frequent water changes are necessary to help improve water conditions.

Fish louse

Symptoms: Disk-shaped parasites attach to the skin. Ulcers often develop close to the area of parasitic attachment. Bacteria or fungus problems may follow after.

Cause: Crustacean parasite. After feeding on the skin, the adult parasite leaves its host and lays gelatinlike capsules full of eggs on the substrate and aquarium decorations. Often the eggs don’t hatch until the aquarium temperature rises, and may stay in the tank for extended periods of time.

Treatment: Remove all parasites from the afflicted fish using a small pair of tweezers. Dab any wounds using a cotton swab dipped in commercial Mercurochrome. Remove water from the main tank and sterilize all decorations and substrate. In other words, start over.

Freshwater velvet

Symptoms: A golden-velvet or grayish-white coating on the body or fins. If your fish has velvet, it looks like it has been sprinkled with gold dust. This disease is very common among certain species such as bettas.

Cause: Piscinoodinium parasite. The adult parasites attach themselves to the skin of tropical fish and then fall off after seven days or so. These parasites immediately drop into the substrate and begin to multiply. The new parasites are then released into the water and move around until they re-infect the fish in your aquarium. If the parasites cannot find a living host within a period of two to three days, they die.

Treatment: Proprietary malachite green remedy. Add 1 tablespoon of aquarium salt for each 5 gallons of water.

Freshwater ich

Symptoms: The sudden appearance of small white spots, which look like little grains of table salt, on the body and fins. Fish infected with this disease continually scratch themselves on gravel and decorations during the advanced stages. (If your fish look like they are making love to the rocks in the tank, they probably have ich.)

Cause: Ichthyopthirius parasite. Adult parasites fall off of the host and multiply in the substrate. Soon after, new parasites search for another living host.

Treatment: Proprietary ich remedy (formalin or malachite green). Even if you remove the infected fish to a quarantine tank, you must still treat the aquarium water in the main tank with medication to kill off any remaining freeswimming parasites.


Symptoms: White growths on the body or fins that are fluffy in appearance and make your fish look like a cotton puff or marshmallow.

Cause: Fungus often attacks regions where the mucus or slime coating on the fish has worn off due to damage by injury or parasites. Once the slime coat is damaged, the fish is more susceptible to all types of other disease.

Treatment: Spot treat with gentian violet, methylene blue, or use aquarium fungicide in extreme cases.

Gill parasites

Symptoms: Redness in the gill areas; labored respiration; scratching; excessive mucus coat; glazed eyes; inflamed gills; loss of motor control (your fish resemble slam dancers).

Cause: Flukes (Dactylogyrus).

Treatment: Sterazin or other proprietary treatment. Formalin baths can be effective as well.

Hole in the head

Symptoms: Pus-filled holes on the head, near the lateral line or the base of the tail. This disease is most common among cichlids.

Cause: Hexamita parasite.

Treatment: Flagyl. Recent findings show that Vitamin A and C supplements are effective in treating this disease (aquatic vitamins, not Flintstones Chewables).

Intestinal parasites

Symptoms: Worms sticking out through the vent; emaciation of the body.

Cause: Several different varieties of intestinal worms.

Treatment: Standard fungus cure or in advanced cases, veterinarian-prescribed anthelminthic added to the daily diet. Add 1 tablespoon of aquarium salt for each 5 gallons of water to help your fish with normal body fluid functions. Remove any activated carbon during treatment. Change 15 percent of the water daily to keep environmental conditions optimal.

Large skin parasites

Symptoms: Scratching; visible parasites.

Cause: Fish lice (argulus) and anchorworms (Lernaea).

Treatment: Remove large parasites with tweezers. Apply an antiseptic solution to the injured site.

Mouth fungus

Symptoms: White cotton like growths around the mouth area (your fish looks like Santa Claus having a bad hair day) or patchy white skin in the same region. In advanced stages, the jawbones begin to deteriorate badly.

Cause: Usually flexibacter, which follows after other infections have begun.

Treatment: Proprietary fungus treatment or methylene blue in the early stages. If this treatment is not effective and the fungus is out of control, consult your veterinarian about antibiotics immediately.


Symptoms: Eyes inflamed and protruding from their sockets to the point where they almost “pop” out of the head. Often the fish’s eyes develop a cloudy, whitish haze. Inflamed eye sockets are also common with this disease.

Cause: Parasites or poor water conditions.

Treatment: There are no known commercially packaged medications to treat or cure this disease. The only thing you can do to help is to improve the aquarium’s water conditions with frequent changes. It may also be beneficial to add 1 tablespoon of aquarium salt per 5 gallons of water to help with osmoregulation (the control of the levels of water and mineral salts in the blood).


Symptoms: Redness at the base of the fins followed by blood streaks that appear on the fins and body. Other symptoms include hemorrhage, loss of appetite, and listlessness. This disease usually follows fin rot or skin infections. Septicemia often results in major heart damage and blood vessel problems. These complications can in turn lead to fluid leakage in the abdomen, which in some cases causes dropsy.

Cause: Pseudomonas or streptococcus bacteria inflames body tissues made susceptible by a skin infection.

Treatment: Antibacterial Furan2 or Triple Sulfa. Change the water every 24 to 36 hours.

Skin flukes

Symptoms: Inflamed skin; excessive mucus coating (your fish looks like it was baptized in Vaseline); scratching.

Cause: Gyrodactylus.

Treatment: Proprietary medication with labeling recommending for skin flukes.

Slimy skin disease

Symptoms: Gray-colored slime on the body or fins; scratching; frayed fins; excessive mucus coat; shimmying like a politician during questioning.

Cause: Costia, trichodina, cyclochaeta, or chilodonella parasites.

Treatment: Proprietary remedy of malachite green and frequent water changes. Short-term (five-minute) formalin and salt baths can be effective. Check and correct any poor water conditions.

Swim bladder disease

Symptoms: Abnormal or irregular swimming patterns (your fish do the doggie paddle upside down) and complete loss of physical balance.

Cause: Bacterial infection; physical injury to the swim bladder from fighting; breeding: netting; transportation from the dealer; poor water quality.

Treatment: Treat with an antibiotic in a clean, shallow tank. (The water should be about 2 inches higher than the dorsal fin on the fish.) Carry out water changes as frequently as once a day if possible.

Tuberculosis (TB)

Symptoms: Fin deterioration; a paling of body color; clamped fins (fins are closed up or folded together); excessive weight loss; ulcers; and pop-eye.

Cause: A highly contagious bacterial disease caused by poor filtration or overcrowding in the aquarium. Many medical personnel believe that this disease can be transferred to humans through contact with the infected areas on the fish.

Treatment: At this time, there is no known effective treatment of tuberculosis, and in our opinion it is not worth risking your own health, or the health of your family, to try treating infected fish. Use strict care when handling these infected fish! Use plastic gloves when removing any fish infected with tuberculosis. Any tropical fish that has this disease should be euthanized immediately.

Why are my Fish Dying - 7 Causes

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There are many causes of aquarium fish disease that are not related to parasites and infection, such as carbon dioxide poisoning, poor water quality, metal poisoning, chemical poison, improper diet, overfeeding, and fright. These important physical and social conditions should be monitored frequently.

1. Carbon dioxide poisoning

Symptoms: Listlessness; increased or rapid respiration — your fish may hang near the top of the water.

Cause: Lack of oxygen; too much carbon dioxide in the water.

Treatment: Add more aeration to improve gas exchange at the water surface; cut down on plant fertilization; check and correct any poor water conditions; and carry out frequent water changes.

2. Poor water quality

Symptoms: The first sign is that your tropical fish are gasping for air at the water surface of the tank and are generally inactive. Clamped or closed fins, overall bad health, and poor coloration are a few more symptoms of incorrect water quality.

Cause: Poor water quality due to infrequent water changes, poor filtration, and overuse of standard chemicals.

Treatment: Make daily water changes until any high ammonia, nitrite, or nitrate levels return to lower readings. Make sure the aquarium has enough aeration and add an extra airstone or bubble disk if necessary. Make sure the pH of the water is within the proper range (a couple degrees of what is normal for the species).

3. Metal poisoning

Symptoms: Erratic behavior; paleness.

Cause: Metal objects coming into contact with the aquarium water.

Treatment: A complete water change. To avoid accidentally poisoning your tropical fish, never allow any metal to come in contact with the aquarium water. Metal hoods and metal equipment clips are two common sources of poisoning. To keep this equipment from poisoning your fish, use plastic clips and make sure that the glass cover on your aquarium fits properly so that no water comes into direct contact with the hood and light fixture.

4. Chemical poisoning

Symptoms: Erratic behavior; gasping for air; fish lying on their sides; paleness; clamped fins; refusal to eat.

Cause: Other common sources of water poisoning in aquariums are cleaning, cosmetic, and insect-control products. Never use insecticides, hair sprays, or mist cleaners near your aquarium. Small drops of these airborne products can easily fall through the small equipment holes in the top of your tank and poison your fish. If you have to use one of these products near your aquarium, tightly cover your tank ahead of time with plastic sheets or large towels to protect your fish.

Treatment: Complete water and filter change.

5. Improper diet

Symptoms: General poor health; paleness of color; inactivity.

Cause: You. Poor nutrition.

Treatment: An unbalanced diet doesn’t contain all the vitamins and minerals important to your fish’s health. Begin feeding a wide variety of commercially packaged flakes, small servings of fresh lettuce, peas, and other green vegetables, and live foods (see Diet and Nutrition Guide for more information on what foods are good for which species).

6. Overfeeding

Symptoms: Lethargic fish; excessive weight gain; and constipation.

Cause: Overfeeding your tropical fish on a regular basis.

Treatment: Fast your fish for two days. Improve poor or fouled water conditions caused by uneaten, rotting food before it leads to more disease problems. If your fish are beginning to resemble the Goodyear blimp and are bobbing up and down in the water like corks, start measuring each serving of food so that you don’t feed them too much at one time (see Diet and Nutrition Guide).

7. Frightened fish

Symptoms: Your fish dash for cover when the aquarium lights are first turned on; constant physical injures from collisions with decorations.

Cause: Sudden changes in lighting, quick human movements, people rapping on the glass, and pets trying to get into the tank.

Treatment: Gradually increase room lighting by opening drapes and turning on lamps before you switch on the aquarium lights.

Home Remedy for Fish - Salt Bath

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salt bath

Here’s a good home remedy that you can try to avoid giving your fish large doses of medications. This method works really well and can save you a lot of money and can cure your aquarium fish disease.

A salt bath as a method of treating freshwater fish has been around since the aquarium hobby first began. Salt baths have proved effective over time to help cure problems such as fungus infestations, ich, and several other types of parasites such as gill flukes.

Basically what happens is the parasites are submerged in the salt solution along with your fish and begin to take on water until they burst and fall off.

We have used this home-remedy method for more than 20 years and have found that it has a very high rate of success in treating different types of diseases.

Don’t try this in your home bathtub with your own sores, or you may end up peeling yourself off the ceiling — you’ve heard of salt in an open wound? Not good for nonfish.

A salt bath is really very simple. All you have to do is add one teaspoon of table salt for each 5 gallons of water in your hospital tank. Continue adding 1 teaspoon of salt twice a day for the first five or six days.

If the infected fish is not completely well by the sixth day, continue to add one teaspoon of salt for another three days.

How to use Quarantine and Hospital Tanks

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A hospital tank helps you treat sick fish and is simply a small aquarium that acts as a hospital ward. You remove diseased fish from the main tank and place them in the hospital tank for chemical or other types of treatment.

It’s as simple as that. A quarantine tank is used to hold fish for a week that you have just brought home from dealer, so that you have time to see if any illness develops before you put them in your main tank. Both tanks are very important.

Advantages of quarantining

All tropical fish go through a tremendous amount of stress being transported to your home aquarium. Think about it, if someone snagged you with a giant pair of panty hose and then stuck you in a large plastic bag, wouldn’t you have a little bit of a problem with that?

Fish are really not that much different from us when it comes to mental stress. A quarantine tank can be the perfect way to provide your new tropical fish with a suitable recovery area — it gives them time to regain their strength before moving into their brand-new home.

Quarantine time

The very first thing that you need to do when you bring your new acquisitions home (unless they are starter fish, the very first fish in a new aquarium) is to place them in a quarantine tank for one week.

You don’t quarantine starter fish because you need them to begin the nitrogen cycle. While your fish are in quarantine, check them daily for signs of disease and make sure they are eating normally.

The tank

We think a 10- or 20-gallon tank is good for quarantining unless you plan on buying some very large fish.

All the equipment you need to get your quarantine tank going is a good-quality power filter and a submersible heater. Make your new fish feel secure by adding some gravel and a few artificial plants.

The last thing you need is for your new pets to go into a bare tank where they can easily be frightened.

Don’t forget that a quarantine tank needs to be cycled just like your regular tank. A starter fish or two helps begin the biological cycle. When you go down to your local dealer to purchase starter fish for the main tank, pick up a couple of extras for the quarantine tank at the same time.

The water conditions (pH, temperature) in your quarantine tank should be similar to those in your permanent aquarium.

This prevents fish being stressed further when you move them to the main aquarium.

How to Set Up a Hospital Tank

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You need a hospital tank to help treat them when they become diseased. Hospital tanks are similar to quarantine tanks. The only difference is, hospital tanks are used to treat ill fish, whereas quarantine tanks are used to hold new acquisitions for observance.

It is much more practical to treat diseased fish in a separate hospital tank because many common medications affect different species in different ways. For example, a malachite green formula used to cure ich in most species has the potential to destroy any tetras in your aquarium.

Treating diseased fish in a hospital tank also lowers the risk of the disease spreading. Many antibiotic treatments destroy essential bacteria and cut down on the efficiency of a tank’s biological filtration system, leading to even more health problems and new diseases. Using a hospital tank prevents these problems.

It really doesn’t take much money to set up a hospital tank if you purchase a small aquarium (5- or 10-gallon) and a simple sponge filter to provide a good base for beneficial biological bacteria.

Filtration systems that contain carbon don’t work very well in a hospital tank because the carbon often absorbs the medication.

The frequent water changes you need to do when treating sick fish are much easier to handle in a small aquarium. A good submersible heater with an internal rheostat lets you monitor water temperature as needed. Diseases such as ich can be treated more quickly if you raise the standard temperature by a few degrees.

Fish Medications 101

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There are a large number of medications on the market, and many of them can be used to treat a variety of diseases, so deciding which one you should actually use can be very confusing.

More often than not, the final choice of medication rests with you. Each case is unique, and many aquarists prefer one medication over another.

In time, you’ll discover which medications work best on certain diseases and different species of fish.

Until you reach that point, try to keep a wide variety of medications around so that your friends and family think that you have everything under control.

The following list gives you an idea of how to use common medications, and the pros and cons of each drug:

  • Salt: Common table salt or marine salt is generally used to treat ich and other parasitic diseases in freshwater fish. The normal dosage is one tablespoon per gallon of water in the aquarium. Salt is very inexpensive, but you can’t use it in tanks containing certain species, such as catfish.
  • Methylene blue: You often use this liquid to treat diseases such as ich, fungus, and velvet. You achieve the correct dose by adding enough methylene blue so that the water is difficult to see through, usually about five drops per gallon. The bluish cast in the water disappears with proper filtration, but stains decorations and gravel, and cannot be used with many species of living plants. Methylene blue is hard to get out of clothes and stains everything it touches.
  • Malachite green: Use this wonderful medication to treat velvet, fungus, and ich. It is very effective in battling disease, but cannot be used in tanks that contain fry (newborn fish) or certain species of fish such as tetras. Malachite green can be very toxic if used in large doses.
  • Formalin: This is a bath-type treatment only and should not be used in the main display tank. This is a great remedy for parasites, but it doesn’t work well on internal infections and can be very toxic.
  • Penicillin: Penicillin treats bacterial infections and is non-toxic. The main disadvantages of this drug are the expense and the difficulty of obtaining it.
  • etracycline: This antibiotic is great for bacterial infections and is nontoxic. The only problem with this medication is that it can turn the water yellow and cause unsightly foam to collect on the water surface.
  • Acriflavine: Acriflavine treats ich and fungus, but may turn the water green.

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