Fish Health

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Aeromonas Hydrophila
Ammonia Test Errors
Anchor Worm
Bacterial Additives
Blanket Weed
Carp Pox
Cat Damage
Costia (killer)
Common Myths
(Egg Compaction)

Fat Fish
Fish Louse
Gill Bleeding
Gill Disease
Gill Maggots
Goldfish Ulcers
Mechanical Fish
Mechanical Injury
Microscope page
Milky Skin
Mouth Cancer
My Fish Jumped
Neon Tetra Disease
pH Crash
Post Mortems
Skin Cancer
Swim Bladder
Tonic Salt
Vitamin C
Water Filters
Water Fungus
White Spot

Fish killed by hypotheria

fish killed by hypothermia

All the headings on the left
have the same affect DEAD FISH.

The result of an ice covered pond, even though water was moving from one pond to another, but 4/5th of both ponds were covered with thick ice - The system owners were away in the big freeze.

Notice how there is no loss of colour - a classic symptom when CO2 has killed the fish. They died by suffocation (like being in a car with exhaust in through the window)

waterfall into pond
If your water temperature is around 4o or below, then ensure that all incoming water is returned below the surface to prevent spashes.

And, on no account net or move your fish - leave them well alone - just let nature take it's course.

Thermal Shock from Waterfalls

At this time of year, the water from your stream/waterfall artificially chills the water. Normally in January and February there is sufficient heat in the sun to prevent the chilling, but not in December. The chilling affects the fish's internal organs and often they cannot recover from this. This year there have already been 20 cases in the last two weeks of fish being killed by the thermal shock from waterfalls. Switch them off until the spring.

Heavy Rain:

When your pond has taken prolonged heavy rain make your sure you do a water change. I do 6" on my 5000 gal pond. You have got to get the acid out of your pond from the rain or you may experience a large pH drop, and we all know what happens then. By the way when did you last check your pH?

Freezing outlets
A big problem with leaving waterfalls running or if the filter outlet is above water, is that they freeze, so sending moving water to waste, and draining the pond. When I arrived at the pond on the left, these outlets where completely covered with ice and water was running behind the pond - it was only good luck I had called on a spot check on my rounds, knowing my client was away out of the country - a few more hours and the pond would have been empty.See also pH crash under ponds

If your filter outlets are under the water surface, and you are worried about CO2 build up, then use an air-stone. Place it in the middle of your pond, about 1 foot under the surface and set it to have a spread of bubbles on the surface of no more than 1 foot.

Become a water keeper first, and a fish keeper second

Warning: formalin will kill your filter. No matter what its says on the bottle always run a by-pass when using this chemical. It will also de-oxygenate your water and when used with alga treatment become toxic to fish.

Salt and Formalin
There has been a lot written and said about this combo. Most of it is complete rubbish.
No1: salt and formalin is not toxic - not at 3% - as most marine treatments are formalin and marine fish are kept at 10 times the salt leval of 3%. Formalin will deoxygenate water and so will salt to some degree. Salt is the best treatment ever found for koi apart from supaverm, (which works even better with salt).
No2: I am not a formalin fan, apart from when it's used with malacite for white spot, as nothing else works> No matter what remedies manufactures would have you believe, what's on the shelves now with the change in the law is utter junk - just colored water - about as much use for fish disease as I have hope of finding oil.

I would not recommend formalin as a treatment on its own, unless you are backed into a corner with salt resistant Japanese costia (buying jap fish is your own fault unless they have been over here for a least a year). The problem with salt resistant costia is that it's a waste of time treating the fish and not the pond. When you put the fish back they will just get re-infected. Costia has got its act together and unless your on the boil, it will beat you every time - one costia for one day = 100,000 or more. If you are told that fish have been tested for costia - now that is a load of rubbish. The only test is quarantine - not the dealers but at your home, and remember, it likes cool water so taking a fish straight from dealers heated water to your heated pond with no quarantine is like bonfire night in a garage.

See our warning on filter containers on the filters page

Now is the time to feed Vitamin C with your food to boost your fish's immune system ready for the cool season.

pond with waterfall
This koi pond had infection after infection until the water fall was cobbled to stop birds bathing and allow drinking only.

Use the links on the left to get more information about fish diseases, and if you're a first time visitor, we recommend you read our Frequently Asked Questions first, as these can often solve common queries.

Download our Checklist a health history questionnaire (PDF file).

The Fish Helpline will help you with your drug dosage - please use the form on our contacts page.

See our decking page (under ponds).

Keep frogs out of your koi pond or problems will arise no matter how well maintained your system may be.

Frogs are said to carry many of your internal parasite problems, see hexamita. Frogs DO carry this parasite, so do BIRDS. Never let birds bath in your waterfalls. Frogs will have been in goldfish and wildlife ponds, dyke lakes or the river next door and can bring infection straight into your pond. You don't have to be a rocket scientist to understand that one. If you want frogs in your garden, which I think is not a bad thing, then have a raised system or a wildlife pond at the other end of garden. Many of our native fish carry infections which do them no harm, but in a koi pond in confined conditions with close fish contact, apart from being against the law - removing fish from native waters - the transfer of infection to koi from native fish is far heavier and faster than a parasite bloom in a pure koi pond. Frog borne disease is a time bomb.

Heron and KoiHeron and Mink

Koi internal organs