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How To Prevent Disease and Water Garden Pond Fish Health Problems

Fish health is a highly specialised subject and there are few vets around who can handle queries on koi or goldfish in a way that gives great confidence. The most important thing any pond keeper can do in the hope that fish diseases stay away from the pond is ensure absolute first class biofiltration. Do not ...

  •  Introduce fish from the wild

  •  Introduce fish from ponds containing unhealthy fish

  •  Overpopulate your pond

  •  Throw in any chemicals of any kind unless you must and fully understand why and have complied exactly with instructions on label.

We recommend that all visitors to this site who wish to learn more about fish heath in general and to discover what can be done to treat fish disease that they visit Ben Helm's web site ... The Pond Doctor for all pond health answers. Having said this, here's a very basic introduction to the topic

Fish Health Introduction

The descriptions of the common fish diseases have been deliberately kept simple to assist the understanding of the basic problems that may be encountered. This is a fascinating aspect of pond keeping and massive amounts of resource for further study can be found across the Internet.

The key to disease control is observing gold fish or koi behavior. Any lasting changes to normal behavior should be investigated because this is the first indication that something in the pond might be wrong.

A correct diagnosis normally needs more in-depth examination often using a microscope.

Larger parasites such as leeches, lice and anchor worms (lernea) can be seen with the naked eye. Fish infested with parasites frequently rub themselves and this is called "flashing" (just as you see mullet flashing in shallow water at the seaside there is a flash of silver from the underside of the gold fish or koi as it turns its body to rub against something).

Other symptoms are localised redness and inflammation on the body of the fish - especially the base of the dorsal fin - as well as breathing difficulties, a general lethargy and ulcers caused by bacterial infection (opportunistic attack). Poor water quality or other diseases can also show the same symptoms.

Always seek qualified help if unsure. Microscopic examination helps.

Fish health in general

As soon as a pond health problem is suspected the first thing to do is to test the water. Test for Ammonia, Nitrite, and pH at a minimum, and preferably also test for Total Alkalinity and possibly Hardness.

Ammonias are lethal in their own right and worse at higher pH. If dead fish exist this will also create ammonia problem. pH can change overnight if the system loses its buffering capacity (this would show on a test of Total Alkalinity). Aquarium Pharmaceuticals basic drop type test kits are believed most accurate according to experts.

In the case of Ammonia accumulation: If water quality is suspect begin a systematic daily changing of 20-40% of the total volume in the system. But beware of major temperature changes in the system. A small addition of salt at .1% level will do no harm.

Secondly, be sure that the water change does not result in electrolyte poor water (as distilled water would be for example). One test of this is the Total Hardness parameter.

If water quality checks show all is OK, but fish are still sick - make sure aeration is good! Add more air if you can.

Ich .... A common but deadly pond fish disease

Ichthyophthirius, more commonly known as white spot or Ich, is a very common fish parasite disease. Ich is characterized by small white nodules on the skin gills and fins. It can affect almost all fish species. The white spot characteristic of Ich forms under the skin or gill epithelium and this has been described as looking like the fish's skin has been sprinkled with salt.

The parasite eats away under the skin consuming body fluids. At the mature stage it breaks loose from the fish's skin and looks for a place to "rest" such as a plant stem. All the while immature Ich are being created and at some stage these hatch, if that is the correct word, and swim around looking for a new host. Once a host has been found the cycle starts again. This means a pond can become completely infected. The life cycle depends upon temperature ... at 25 degrees C (75 degrees F approx) it is around 1 week whilst at 10 degrees C (50 degrees F approx) it takes much longer ... about 5 weeks or so. This means treatment has to be continued over a period of time and is one reason why salt is good. Salt is largely unconsumed nor is it oxidized in the pond environment. Salt concentration should be maintained at about 0.3% level

Apparently while under the skin of the fish there is a total resistance to almost all common cures. However in the other stages Ich succumbs readily to salt solution treatment. If Malachite green is used be aware that this is a dangerous chemical and perhaps a carcinogen.

Tissue damage and particularly with respect to the gill regions is a significant threat to the health of the fish and makes the fish susceptible to other potentially lethal bacterial diseases.

New fish (when not quarantined) are the most important source of initial Ich infection. Ich is most often brought into the tank or pond on new fish or plants (not if they are quarantined!). Subsequent stress or poor pond water conditions can awaken white spot to re-infect either its host or other fish.

Costia & Chilodinella Head

These are parasites of freshwater fish that can be responsible for mass destruction of goldfish in a small amount of time. Salt again is the solution. Costia can attach themselves or swim freely. When attached they look like small "commas" stuck to the gill or skin. If a lot of goldfish are dying then be suspicious of this disease.

Chilodinella is a heart shaped organism, or a large round organism full of tiny bubbles. Chilodinella succumb easily to salt treatment at 0.3%. 14 days treatment is recommended and make sure air is used profusely to compensate for gill damage. If goldfish are dying on the surface in large numbers then suspect Chilodinella.

Flukes Head

Freshwater flukes are microscopic in size and are reported as Gill Fluke, and the second class is the Skin fluke. Gill flukes lay eggs and the rate of egg laying is a function of pond temperature ... low temperature slow rate and vice versa. The incubation within the egg is also temperature dependent. Flukes attach themselves to hosts in the gill region. Skin flukes produce live young which immediately infect the host. The rate of reproduction is very high.

Flukes feed on blood and mucus close to the surface of the fish's gill or skin. Skin flukes are happy to reside in the gills as Gill flukes are to live on the skin. They use hooks and/or suction to remain attached to the host.

Flukes survive in 0.3% salt solutions. The main cause of fish deaths seems to be related to secondary bacterial infection from Aeromonas and Pseudomonas types.

The oxidation and disinfection characteristics of Potassium Permanganate are able to control flukes at the level of 0.2%.

Some recommend the use of formalin but this has a severe negative effect upon bio filter bacteria and should be avoided if possible.

Anchor Worm & Lice

Argulus is a crustacean parasite commonly found in ponds. They are greenish disc shaped organisms with suckers and small legs. These parasites transmit Aeromonas and other bacteria thereby infecting the fish they bite. Treatment is by specialized chemicals.

Lernea elegans is the most common type of Anchor worm affecting Koi. They multiply rapidly creating wounds which are then invaded by Aeromonas bacteria. This is the real problem.

Bacterial Infections:

Bacterial infection within fish shows itself as one of the following normally

  •  reddish lesions in the body or fins

  •  swollen eyes

  •  red mouths

  •  red stomach region

  •  unknown death reasons

The result of bacterial infection is normally septic wounds such as ulcers.

Antibiotics find a place in the treatment of koi or gold fish but this is best done under close and expert supervision bearing in mind that bio filter operation will be severely compromised. It is often best to treat the gold fish or koi fish in a separate bath rather than in the fish pond itself ... in hospital as it were.

Bacterial infection often results from initial infections by parasites of various kinds and also poor pond water quality in general which in turn creates further opportunity for parasite growth. This should emphasize the absolute importance of good pond bio filtration accompanied by regular cleaning of bio filter media along with the avoidance of bacteria traps such as the sand in sand filters. Always remember the critical importance of aeration in well cared for koi or gold fish ponds.

Bacterial infection in gold fish or koi ponds can be avoided to a great extent by using modern specialised products using the process of competitive exclusion ensures that Aeromonas and Pseudomonas in particular are starved out of existence rendering the gold fish or koi safe from attack.

Ulcers which are an indication of advanced bacterial attack can be caused by damage to the skin from parasites or exposure to high levels of ammonia or nitrite and/or high or low pH ... bad water quality. Under these circumstances bacteria thrive and the induced stress levels make the gold fish or koi disease prone.

If a single gold fish or koi is affected then that individual may have a specific problem. In the case where numerous gold fish or koi have the disease then there must be underlying problem within the pond.


Dropsy is a term used to describe the swelling of a fish's body. This causes the scales to stand away from the body - this is why it is also called pine cone disease. Dropsy is perhaps most common in goldfish and koi. If the fish has a sore, and the scales around the sore, or even on the whole side of the fish, stand up, it does not necessarily mean Dropsy. These fish may respond well to injections of antibiotics. However if a fish does have fully developed Dropsy then survival is unlikely.

Dropsy is a serious, and usually lethal condition brought on by stress inducing factors like sudden water temperature changes and poor water quality. Go back and re-read about biofiltration.

Expert advice should be sought but recovery from true Dropsy is highly unlikely.


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