Koi Care, Disease and Treatment

Koi carp and goldfish are typically very hardy fish. They become ill usually due to poor water quality , stress and sometime introducing new fish to pond. It is extremely important you have adequate filtration to break down ammonia and nitrite. Partial water change is also very important , at least once in two weeks. Filtration capacity should always be enough to manage approximately triple the amount of fish in pond. A source of carbonate should always be present unless you add them regular, either inside or outside filer. This could be calcite rock (non crystalline/brittle type), oyster shells etc. Breakdown of ammonia into nitrite requires much more quantities of carbonate molecule than oxygen molecule therefore it is essential you have a good KH value, minimum 4 or higher to avoid troubles (7 or 8 recommended). When KH is good, PH value will not fluctuate too much to stress fish.
Stress is the most common cause of fish diseases. Stress can be caused by many different reasons. Most common ones being , poor water quality, parasites, new fish that already stressed from travelling etc etc. Adding pond salt at a rate of approximately 3kg per 1000 litres of water will help fish recover from stress more easily. It is recommended you add salt no more than 1kg/1000 litre per day.

Water change

Weekly water change is very important. Pond under 5000 gallon may need roughly 10% while over 5k gallons may be sufficient with 5% weekly change. Higher fish load will require higher percentage of water change.
Public water most likely will have chlorine and sometime chloramine, both of which are harmful to fish. It is essential these chemicals are removed before adding to fish pond. Cartridge and liquid dechlorinators are most common for this purpose. Water can be filled to a stock tank and aerated with air stones etc for roughly 24 hours to eliminate chlorine but chloramine will require chemical to neutralise. New water temperature and parameters are also very important to reduce stress on fish. Trickle in trickle out system with inline dechlorinator can be best.
Water change during winter will depend on temperature, below 6 or 7 Celsius I would carefully change water may be once every 3 to 4 weeks. If frequent rain water falling on pond it may not be necessary to change water at all BUT I would check PH or KH and add KH buffer if necessary (most likely it will be) as Rain water can lower PH to dangerous level for Koi fish.

Using rain water for water changes

Pond owner facing high cost from using city water can take advantage from harvesting and using rain water to do their weekly water changes. This is probably the best way forward and should be considered seriously. This will also lighten the stress on our city water suppliers.

We need to choose correct type of harvesting tank. Water tanks which are safe for drinking water is also safe for fish. There are a lot of rain water tank which are NOT safe for drinking water and those are also NOT safe for fish.

Rain water quality/parameters will differ from area to area and will require “conditioning/processing” before using for fish pond. This may be less of a problem for regions with minimal air pollutions. There are a lot of undesirable elements that can come with the rain e.g. acid, toxins, pollutants, parasites, bacteria and fungi but we need to learn how to deal with them and not just waste this opportunity. Here’s what I would do.

Make sure no debris or mosquitos enter harvesting tank. Fill harvesting tank to approximately 2 to 3% of its volume with different type of calcium carbonate stones e.g calcite, limestone, CAC03 (calcium) stones etc ( wash all stones thoroughly before adding to tank). Add air stone for aeration 24/7 (if possible/highly recommended), a small, low power consumption air pump dedicated for this tank is ideal. Air stone can be placed a foot under water as small air pump will struggle with higher depth. Test water for PH and KH from time to time so we have a good understanding of how acidic etc water is through out year. Use cheap bicarbonate of soda to adjust KH/PH level if necessary and I would aerate at least 40/50 hours before using for pond water changes. Having lots of caco3 stones and aeration may be sufficient for balancing PH & KH . This process will get easier with time and most importantly save a lot of city water throughout our world.


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Two treatments, before winter and in spring to stay ahead of parasites

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Listed below are 25 most common koi diseases and possible treatments but first I like to give a very new approach to deadly resistant flukes, a nightmare for koi hobbyist around the world.

Please note all medications are administered at your own risk. You must calculate your pond WATER volume accurately. I have seen too many times hobbyist calculating this wrong. I will talk about this in a separate article. Extra aeration is highly recommended during treatment.

I experimented with many different fluke treatments available on market. All of them produced some good results but they were back within weeks. I found Lernex Pro was one of best so I carried on experimenting with Lernex pro by increasing doses carefully. Experiments were carried out on four different ponds with resistant type flukes, both body and gill flukes.
Please keep in mind all medication degrades over time by oxidation, bacterial activity in your filter and pond. I added more Lernex Pro on a daily basis to keep up its strength and not leave it for a week or two then add second dose as I did previously following the instructions. Two courses of lernex pro at temperature 17 degree Celsius to 20 degree Celsius. After completion I scraped fish once every two weeks for 14 weeks and there was NO flukes. All medications must be used with manufacturer instructions. I did something different as flukes were coming back no matter what treatments used. This is what worked for me so I am sharing.

The method

switch off UV light, take out any carbon filter or zeolite etc
Body fluke and gill fluke method below. Please note gill fluke lays eggs and medication will not effect them so you need to repeat dose when they hatch.

Gill fluke egg hatches in around 4 days at 20 degree Celsius, 6 days at 17 Celsius, 12 days at 12/13 Celsius, 19 days at 10 Celsius.

Chloramine-T can be used a day before treating with Lernex Pro, please see Chloramine-T section below for dosage instruction

Day 1. add a full dose (1 mil per 20 litres of water) plus 20% extra. example, 5000 litres of water will need 250 mil plus 50 mil total 300mil of lernex pro
Day 2. add 10% ish of the full dose you added on day 1
Day 3. add 10% ish of full dose
Day 4. add 5% ish of full dose
Day 5. add 5% ish of full dose
Day 6. add 5% ish of full dose
by end of day 6 you should NOT have any body or gill flukes. In fact, most flukes were dead after 24 hours but some can hide in places where treatment don’t reach at full strength so 6 days later you can be confident they all dead with above method.
Now you need to deal with gill fluke eggs that are hatching day after day depending on WATER temperature. At 17 celcius or above 2 full course treatment (1 course being dosing from day 1 to day 6) more than sufficient.
Nothing on day 7
Nothing on day 8
Nothing on day 9
Nothing on day 10
Nothing on day 11
Big Water change on day 12 (please note: big water change can be very stressful to fish if new water temperature and parameters are different), I did approx 40%. Please do NOT use liquid dechlorinator or anything that will interfere with treatment, i.e. neutralize lernex pro
Day 13 you start dosing again as above for 6 more days but without the 20% extra you added on day 1
From 10 Celsius to 15 Celsius you must do 3 doses (without adding extra from day 2 to 6). Only adding treatment at day 1 including 20% extra then repeat every 12 to 15 days.
If water temp below 10c treatments will not be as effective but you cannot leave flukes to destroy your fish. In this case you can add pond salt (or any cooking salt but not table salt) at rate of 6kg per 1000 litre of water but NOT all at once, I add salt no more than 1kg/1k litre of water per day. example 5k litre of water will need around 30kg of salt. Then dose with lernex pro WITHOUT adding extra on day 2, 3, 4, 5 and 6.

Lernex Pro dosage and result from another pond

Note: heavy resistant type fluke infestation. Flukes were coming back no matter what treatments used, both body and gill flukes. Temperature 17 to 20 Celsius.

Day 1. Added a full dose plus 20% extra Lernex pro

Day 2. nothing

Day 3. added 30% of full dose I added on day 1

nothing on day 4 to day 10

Day 11. big water change

Day 12. added another full dose of lernex pro but no extra like I did on day 1

Results, No flukes, I scraped fishes once every two weeks for 14 weeks.

Finally one more interesting and successful Lernex Pro Treatment.

Note: Resistant type, both body and gill flukes. Temperature 17 to 20 Celsius

Day 1. Full dose of Lernex pro

Day 3. added 50% of full dose.

Day 8. big water change

Day 9. another full dose of Lernex Pro

Day 13. added 20% of full dose

Result, same as above, NO more flukes.

Three common reoccurring parasites.

Next I like to highlight three of the common parasites that can appear through out year. Costia, Trichodina and Chilonodella. These are easy to deal with compared to deadly resistant flukes. As with most if not all parasites the symptom’s become clear as they spread and multiply in numbers. It is extremely important you act soon as you think there may be parasites. A microscope is essential for all koi keepers.
Hobbyist who do not have access to microscope or it is difficult to get your fish scraped you can follow the all in one solution below if you see symptom’s and suspect there are definitely parasites on your fish.

The all in one solution.

FMG. Formalin and Malachite Green. You can buy them separate or ready to use mixture from any reputable brand.
A little note, many different name and brand of treatments have been introduced around the world. Many hobbiest do not use fmg and reaching out to new names and treatments with higher price tags. I like to take a different view and go back to basic with added instructions on how to use fmg that will be deadly against parasites.
Tow doses of FMG, 5 to 7 days apart/ manufacturer instruction (please calculate pond water volume accurately) will eradicate most parasites including costia, trichodina , chilonodella etc. (temperature dependent, at 12 Celsius or above, no salt with formalin although i tested with up to 0.15% salt while dosing with fmg with no apparent side effect). Please follow the instruction that comes with fmg. So why koi keepers report fmg not working ? It is because fmg (same with most other treatments) is being neutralised by many variables in pond water. You need to add more on day two of the first dose of fmg. I usually add another 15 to 20% more fmg on day two. This simple adjustment produces highly effective results.


After administering any medications, ulcers may appear on fish. This is NOT necessarily because there are parasites but it is the damage they have done to fishes body. It is bacteria causing a secondary infection. Bacteria itself do not cause ulcers but damages left by parasites where bacteria sets in and carry on causing more damage. This is where salt is highly effective. 3kg to 5kg salt per thousand litre of water, thus 0.3% to 0.5% salt can protect fish from secondary infections and help heal quickly.

If you have any heavy infestation of parasite outbreaks, ulcers almost certainly will appear. Please give your filters a good clean, do a water change and add salt as above rate. This is usually the cheapest, easiest and one of most effective method to treat ulcers. If ulcers are too bad you can use topical treatments available from koi dealers. Alternatively you can take salt concentration to 0.65%, thus 6.5kg salt per 1k litres of water. I usually maintain high salt until ulcers healed/new skin formed.

Ich (appears like little white grain of salt on fish)

This is a very common parasite that is usually born out of poor water quality. Ich will feed on your fishes body for approximately three weeks then detach themselves and fall to the bottom of pond for reproducing. Heavy outbreak of ich likely to leave ulcers behind therefore salt may be the best approach. Filter clean, water change and take salt to 0.6% thus 6kg of salt per 1k litre of water. I would maintain this salt concentration for 5 to 6 weeks. Alternatives are fmg, malachite green and formalin. A total of 3 doses may be required. …..to be continued….

Chloramine-T to treat most parasites

Chloramine-T can be highly effective treating any fish ailments. It can also be very disappointing against parasites. Here’s why

Chloramine-T is effected by water hardness and PH, for example

2.5 gram per 1000 litre in soft water with PH 6.0 will have similar effect as 15 gram per 1000 litre in hard water with PH 7.0

Dosage difference with water hardness and PH is so huge that you can easily KILL all your fish using higher dosage in soft water with lower PH. It is the opposite and disappointing result against parasites if you use lower dosage for hard water with higher PH.

I have used Chloramine-T, successfully, to treat many parasites and fungal diseases like costia, trichodina, chilodonella, cottonwool diseases etc with five consecutive treatments over five days. Each dose was 8 grams per thousand litre of water. This dosage (8g/1k litre) can be used safely with PH over 7.2 for various other purposes like stripping off slime coat, reducing bacterial level in pond, fungus and many common parasites (6 gram/1k litre of water if PH is 7 to be on the safe side). I have used this dose a day before using fluke treatments, it is highly effective.

Dosage above mentioned may effect the filter bacteria slightly

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