Koi & Goldfish Health

Did You Know That There Are Fish Veterinarians?


If you are in need of immediate help with your pond, you can go to the American Association of Fish Veterinarians website and find a Fish Veterinarian in you area with a simple search. 

Wage a war on fish disease.


Bacterial problems with Koi and Goldfish can be a common occurrence. What is not commonly known is that these problems are typically a secondary or tertiary result of other environmental issues. Helping fish heal their wounds is a multi-step process. A great analogy is fighting a war. In a war, soldiers are placed in an environment (the battle ground). When there is no stress or fighting with the opposition, the soldiers stay fairly healthy. They may get a headache or a cold or other minor sickness… but in general if the environment is good, the soldiers stay healthy. 


Ok, in pond terms, Koi and Goldfish are pretty healthy tuff fish. Koi are essentially river carp (Cyprinus Carpio) and are designed to withstand a lot of environmental factors. Goldfish Carassius Auratus are a close cousin. When they are in a pond stocked with the correct number of individuals, and are fed a quality diet, and receive proper filtration, they will thrive and grow. When the conditions are not favorable… for a length of time, they can succumb to sickness. This can be put into terms of war using the following thoughts. 


Things that cause stress in Koi and Goldfish:


Water Quality. Ammonia, Nitrites, Low mineral content, High Bad Bacterial counts/Debris in water:


High Ammonia and Nitrites both affect the fish’s ability to breathe/absorb oxygen. Think of it as being slowly choked or breathing smog to the point of sickness. If your body is weak, you get sick more often. If you are very weak/sick, and the environment is not corrected, you get weaker and sicker. To correct high ammonia and nitrites short term,  a water exchange with dechlorinated /de-ammoniated water, of the same temperature, should be done. Another emergency option is to use an ammonia binding chemical such as Pond Amquel Plus or zeolite to block the effects of ammonia. Nitrites are typically caused by the breakdown of ammonia by good bacteria in the bio-filter. They are further broken down to Nitrates that are relatively harmless at common levels. Nitrites, at elevated levels, can cause breathing problems in Koi and Goldfish. This can be helped by adding salt at 5 pounds non iodized pond salt per 100 gallons of water. Just remember that salt will harm/kill pond plants that if allowed to die, in the pond, will be another source of ammonia. 


Long term cure for ammonia and nitrites include the use of a correctly sized bio-filter that receives pre-filtered water containing no solids. Maintain the calcium and bicarbonate levels (alkalinity and hardness) that are needed for the bio-filter to “eat “ the ammonia and nitrite. Maintaining water quality is like humans living in a place with fresh air and overall good environment. It is the first and most important step in maintaining fish health. Checking water quality and levels is done with fairly easy to use liquid test kits. They include a sheet with acceptable levels to compare. Every pond owner should have and know how to use a water quality test kit.




Parasites are the little bugs that live on and in our bodies. We all have them present all the time. Typically in small quantities that are tolerable and not noticed. When the environment is correct and the fish or soldiers are under stress, the opportunity presents itself for parasites/disease to flourish and expand to the point where it affects the fish/soldiers. These little “snipers” bury into the skin of the fish opening up a place for the third portion of disease to occur. They can be controlled by prevention, quarantining new fish in a separate tank/pond for two weeks prior to adding to the general population.  Several types of parasite control chemicals can be used to reduce parasitic numbers. The most effective for over 80% of freshwater parasites is pond salt at 5ppt or point five percent or 5 lbs per 100 gallons pond water.  Parasites are common and not typically an issue unless they are given the opportunity to thrive. Parasites are the “snipers” that shoot holes in our “soldiers”. Less opportunity for “snipers” means less wounds to heal.




Bacterial ulcers and mouth rot, that are noticed by the pond owners, are the most and the last occurrence prior to the possibility of fish dying. This is much easier to see (ulcers) than the undetected poor water quality or microscopic parasites. Each condition has its signs but they are typically missed by the pond owners. Bacterial issues can be cured by a multi  step process. First fix the environment (water quality) second reduce snipers (parasites) third use medications designed to stop the bacteria from growing  (typically an antibiotic in a medicated food such as Blackwater Creek Medicated Ornamental Fish food). Feed for 10 days continuously.




Providing your fish a healthy well rounded environment is equally important. Your pond fish rely on the food you provide for over 90% of the nutrients they receive. The other 10% is derived from grazing on the algae and insect life in your pond. If you feed your “soldiers” a diet of junk food continuously, they will slowly develop health issues of various type that lead to further stress and disease. Feeding a well rounded diet such as Blackwater Creek Koi Foods will ensure they receive the right amount of nutrients to allow them to thrive.


So keeping fish healthy is akin to war. Take the “soldier” out of the stressful environment. Remove the “snipers” shooting gunshot holes. Heal the holes before the bacterium has a chance to do more harm or cause death. It is a multi step approach. Very rarely is there a “ah ha” item that is the single cause of disease issues. It is just the last portions of the problem that is typically noticed.


Here are some items to note:


Koi and Goldfish thrive at optimum temperatures around 75 degrees. They can withstand 33 degrees to 95 degrees. Warmer temperatures allow chemical and biological processes to happen quicker. Chemical reactions double for every 10 degree increase in temperature. Large amounts of debris, waste or uneaten food may produce ammonia at levels that your filters cannot handle. Seasonal pond cleaning and frequent pre-filter cleanings will help.


Antibiotics work by stopping the reproduction of bacteria, not killing it. Similar to having a rodent infestation. If we were to sterilize the rodents so they could not breed/multiply, they would eventually die of old age. Antibiotics work the same way. It is important to feed antibiotics for 10 days continuously to ensure the bacteria do not get a small ‘taste” of the medicine that could allow them to become resistant (think of vaccination using very small amounts of a substance).


Fix the water quality and add salt is the most often recommended first step in helping fix Koi and Goldfish disease issues. Mouth rot and ulcers or holes are typically the last thing to occur in a series of factors leading up to a fish death. The earlier these factors are cured, the better chance the fish has to heal and thrive.


Keeping Koi, Butterfly Koi or Long-fin Koi and Goldfish is fairly easy. They are very robust fish that will bring years of joy to your backyard. Keep them happy and healthy.