Ich parasites of gold fish and koi
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.
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 s 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.
Dr Erik Johnson of koivet.com has provided the following salt treatment schedule to remove Ich ...
Remove valued live plants.
2. Raise temperature to 80 degrees F (26 degrees C max), tops.
3. Increase aeration! ... always important in any stress situation
4. Add one teaspoon of salt per US gallon.
5. Twelve hours later, add another one teaspoon of salt per US gallon.
6. Twelve hours later, add another one teaspoon of salt per US gallon.
7. Within 48-60 hours of the second salt dose at 80 degrees, the Ich will be gone.
8. Leave salt in the water for another 3-5 days unless you're worried about your live plants.
9. Remove salt via partial water changes. (30-40% at a time if desired).
To convert to Imperial gallons the factor is 1 Imperial gallon is 1.2 US gallons
What to do if you suspect disease problems
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 most accurate according to experts. Review USA on-line pond supplies
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 the system. A small addition of salt at .1% level will do no harm.
Articles on Koi & Gold fish medical conditions