As one of the rising stars of the hobby, the flowerhorn has attracted many enthusiasts. Many are choosing to start with this fascinating fish, and Philippine Arowana and Luo Han Society’s (PALHS) Mark Timothy Libunao generously shared his time and resources with Animal Scene’s readers regarding treating the various health problems of this man-made fish.

Text by Mark Timothy Libunao
With additional text and editing by Charlene Bobis

Hexa Infection (Hexamitiasis)


Also known as “hole in the head” or HITH, this disease is caused by a parasitic protozoa (hexamita, usually Hexamita salmonis and Hexamita truttae) in the water. This is an opportunistic organism that lives in the water and infects fish, particularly those with weakened immune systems due to overfeeding. The disease is characterized by the flowerhorn excreting white feces, a decrease in the fish’s appetite, and the characteristic holes in the head easily visible even at a short distance in the latter stages of the disease.

Infection stages 1. (Early) At the early stages (first to third day of infection), the flowerhorn is still agile and aggressive. Color intensity and pearls are normal, as is appetite. There is almost no sign of disease except for one important manifestation to look out for: the passing of translucent, thick, white and string-like discharge with rounded beadings along the length of the string. This signifies that the fish’s intestines are irritated by the parasite’s presence; hence, the lining is being shed.

One should take note though that not all flowerhorns that excrete white, string-like poop have a hexamita infestation. Flowerhorns that are exposed to new tank water or a new diet usually shed intestinal lining, but this is only limited to a day or two. If the white, stringlike poop continues beyond two days, the possibility is high that your fish has hexamitiasis. The difference though between the shedding of intestinal lining between hexa and non-hexa poop depends on the manner the lining is being shed.

If the white string-like poop is long, continuous, non-terminating, and usually tends to hang over the cloaca or anal area, that signifies a hexamita infection. If the white poop is cut off and short, then it’s a simple intestinal irritation because of the introduction of a new diet or new water environment parameters.

2. (Intermediate) The progressive stage of infection is during the fourth to eighth day of infection. Agile mobility is slowly disappearing. The fish loses appetite, refuses to eat, and the vibrance of its colors fades to dull. The fish usually swims less and tends to stay in one place; this is because of the loss of body energy from having no food intake coupled with the continuous intestinal lining shedding. Body mass volume is still normal to slightly hyposthenic.

3. (Final) The late stage of the infection is the 14th day onwards. The fish’s mobility is severely affected due to intense shedding of intestinal lining. The loss of body mass is severe, with an apparent spread of the parasite to the body cavity and the head, causing the widely known disease manifestation: holes in the head.

The medication: The drug of choice for treating this infection is Metronidazole Anti-Protozoal medication.The amount of the drug to be given depends on the fish’s size and the manner of administration of the drug. There are three methods available depending on the condition of the fish and convenience of the owner (more on this later).

Contamination warning: Hexa is contagious, so be careful not to mix the tools and accessories used for in fishkeeping. Fish tools and tank accessories used in hexa management (such as nets, hoses, fliters, and OHF) should not be used for healthy flowerhorns as these can transfer the disease to them.

General treatment instructions:

A hospital tank should be used, preferably 5-10 gallons in capacity to save on water and other regimens every water change. One metronidazole tablet is prepared in a 500 milligram (mg) dosage. Powderize the tablet into fine granules and dissolve it in 5 milliliters (ml) of water. Make sure the powder is completely dissolved to equalize the dose per ml of solution. Actual formulation after the tablet is dissolved is 100mg per 1ml.

Method 1: Drug Mixture with Fish Pellet (For use during the early stages of the disease, while the fish is still eating). Achieves faster results as drug dosage is at the maximum with no drug wastage.

Dosage based on fish size, measured tip to tip:
• 2-3 inches – 10mg twice a day or 0.10ml per dose
• 3-4 inches – 25mg twice a day or 0.25ml per dose
• 4-5 inches – 50mg twice a day or 0.5ml per dose• 5-6 inches – 75mg twice a day or 0.75 per dose
• 6-7 inches – 125mg twice a day or 1.25ml per dose• 7 inches up – 200mg twice a day or 2ml per dose


Aspirate the desired amount of drug into a syringe (remove the needle, and use a tuberculin syringe for dosages less than 1ml). Place the drug solution into a small bowl or container. Add the daily pellet consumption of the fish and allow the pellets to absorb the drug solution.

Feed the fish. Continue regimen until symptoms disappear and normal mobility and aggressiveness is back.

Method 2: Direct Feeding (For use during the progressive to late stage, when the fish is not eating).

There will be some drug wastage as not all of the drug administered orally will be taken in by the fish. Some will escape the mouth and drip down to the gills. Recovery will be slightly slower compared to that of the drug mixture with fish pellet method.

Dosage based on fish size, measured tip to tip:
• 2-3 inches – 10mg twice a day or 0.10ml per dose
• 3-4 inches – 25mg twice a day or 0.25ml per dose
• 4-5 inches – 50mg twice a day or 0.5ml per dose
• 5-6 inches – 75mg twice a day or 0.75 per dose
• 6-7 inches – 125mg twice a day or 1.25ml per dose
• 7 inches up – 200mg twice a day or 2ml per dose


Aspirate the desired amount of drug into a syringe (remove the needle and use a tuberculin syringe for dosages less than 1ml). Take the fish out of the tank and place it on a thick cloth to cushion its body.

Using the tuberculin syringe, measure the length of the fish gut from mouth to stomach by situating the syringe above the fish, which should be lying on its side. That should guide you on how much of the length of the syringe you can insert into the fish’s mouth. Insert the syringe into the mouth slowly as the fish breathes until you have reached the desired length. Slowly feed the drug. Continue regimen until symptoms disappear and normal mobility and aggressiveness returns.

Method 3: Tank Water Infusion. The recovery rate for this is relatively slow as the dosage ranges from a minimum of 125mg to a maximum of 250mg of metronidazole per 10 gallons per day.


Directly pour the prepared drug solution into the tank water. Water change should be 50% every day, with subsequent addition of 50% of the drug dosage placed the previous day.

Additional instructions for all methods:

1. Use an aquarium heater and set the temperature to 32 degrees. Use a 75-100 watt heater for 5 and 10-gallon tanks and 150 watts for 20-gallon tanks.

2. Add 200 grams of rock salt for every 20 gallons of water.

3. Add 4 drops of methylene blue (for progressive and late stage) to prevent the survival of other opportunistic organisms like fungi that can cause white spots.

4. Water change should be at 50% every day. For methods 1 and 2, add 50% of the amount of salt placed the previous day to maintain tank pH at maximum. (For example, if the amount of salt placed in the water the day before is 200g, add 100g during the succeeding water change). Do the same with methylene blue (if fish is in the late stage of the disease).

For method 3, a 50% addition of the original drug dosage placed in the water on the previous day should be done. Other treatments:1. Alternative treatment: Azoo Anti-Endoparasite. Follow instructions on label.

2. A new treatment modality:

Prepare the following:

• 3 pieces Metronidazole 500 milligram (mg) tablets
• A 15-gallon tank
• A heater If no 15-gallon tank is available, you can use bigger tanks, but make sure that the water content is only 15 gallons. Use of smaller tanks is not recommended as the procedure requires a daily increase in dosage. Smaller tanks contain smaller water volumes; hence, the procedure can result in an overdose if smaller tanks are used.

Treatment steps:

Day 1: New water set-up. A 100% water change should be done before doing the procedure. Set heater at 32 degrees. Drop 1 metronidazole tablet inside tank. Siphon poop. Do not feed.

Day 2: Same set-up. Drop another metronidazole tablet inside the tank.

Day 3: Same set-up. Drop 1 metronidazole tablet inside the tank. The total number of tablets dropped into the tank over three days should be 3.

Day 4: Same set-up. No more addition of medication.

Day 5: 100% water change. Test feed with 1 pellet. If the flowerhorn feeds, then it has fully recovered. If not, repeat steps from Day 1.

(Source: You can learn more by searching the hashtags #FHempPH #isdiagnosis)



Pop eye or cloudy eye is a manifestation of dropsy. Dropsy is an internal infection of the fish caused by poor water parameters, usually as a result of increased nitrates secondary to neglect in cleaning or replacing tank water, media or substrates or putting too much salt in the tank water.


The infection has already rendered the kidneys and other organs ineffective; therefore, there is already an imminent water retention which is already manifested by the popping of the eyes. Adding salt will only make it worse as it will cause more fluids to accumulate inside the body and cause more edema.

Treatment steps

1. A hospital tank should be used. 10 or 20 gal tanks are the most appropriate. Do not use smaller tanks as these will only hinder fish movement and aggravate the situation. 20 gals is the recommended size.

2. A tetracycline class of antibiotic should be used. 500mg of tetracycline (or doxycycline, minocycline) should be dissolved in warm water then mixed with the tank water.

3. Perform a 100% water change every 2 days using only aged water. Replace antibiotic. Follow step 2.

4. Use an aquarium heater and set it to 32 degrees Centigrade.

5. Minimum treatment period is 2 weeks.

6. It is recommended to place Methylene blue in the tank water to control fungal infection. At this point, the fish is immune-compromised and a fungal infection is most likely to develop. Add 5 drops of Methylene blue per gallon of water.

White Spot

White SpotTake

Ichthyophthirius multifiliis is more commonly known as freshwater white spot disease or freshwater itch. The causative agent is a protozoa and not a fungus or mold as commonly misunderstood by many.

Predisposing factor: Fish with lowered immune systems due to sudden water parameter changes, overfeeding, or high nitrates in tank water secondary to filters or substrates that are not cleaned. Manifestations: White spots on the head, the body or the fins. The white spots can either be solitary or multifocal.


1. Take the fish out of the tank.

2. Do a 100% water change with aged water.

3. Get a cotton then remove the slime over the fish body. Get another cotton, soak it in methylene blue then wipe the area affected with the methylene blue.

4. Put the fish back in the tank with new water. Add 5 drops of methylene blue per (1) gallon of water.

5. Add rock salt. 20 grams or 4 tablespoons of salt per 20 gallons of water.

6. Set heater at 32 degrees centigrade.

7. Do a 100% water change every two days then repeat steps 1 to 6 until white spot is gone.

If the fish affected with white spot shares tank space with other fishes, you might as well expose the other fishes to the same treatment EXCEPT the wiping of the slime and methylene blue over the body. Just let them swim in methylene blue affected water together with the other tank mates. It’s called a “prophylactic treatment” since they were also exposed to the same condition as the one with white spot.

Swim Bladder Disease

Swim Bladder Disease

Most often characterized by the afflicted fish swimming sideways or even upside-down, swim bladder disease isn’t a laughing matter.

Common to aquarium fish, this disease is most often caused by two factors: constipation resulting in impediments in the swim bladder or infection of the swim bladder organ itself. It can also be caused by both factors.


Routine swim bladder treatment includes the following:

1. Transfer fish to a hospital tank. A 10-gallon hospital tank is recommended.

2. Reduce tank water quantity up to the level where the fish can remain afloat to reduce stress on it. Usually, if a 10-gallon tank is used, half of the water is removed.

3. Add epsom salt. Maximum dose is 2g per gallon; 1 tablespoon is 20g. If you are using a 10-gallon tank, your tank will have 5gals of water left, and the amount of epson salt to be used is only 10grams. Do not overdose as this can cause loosening of the intestinal tract and make your fish prone to hexamita infection.

4. Use tetracycline to combat possible infection (85% present in all SBDs). The recommended dose is 500mg per 20 gallons. To get the exact dose for your 5-gallon tank water, you need to dissolve tetracycline in 20ml of warm water. Then get 5ml and pour it into the tank. Dissolve the remaining 15ml. You cannot use this anymore.

5. Use a heater set at 32° Centigrade. Do not feed the fish anything.

6. Leave the fish in this set-up for 5 days and do a 100% water change on the sixth day. Repeat procedure if necessary.

This appeared in Animal Scene’s June 2016 issue.