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Diagnosing Your Fish

Is your Fish showing symptoms of an illness? Please check here for symptoms, information and various treatments for problems that fish may face.

20 August 2020
Diagnosing Your Fish

For many pond keepers their fish have become part of their family, growing up alongside their children and developing personality characteristics. However when fish develop health problems, they can’t be taken to a vet like other family pets. It becomes the Pond keeper’s responsibility to diagnose and treat their aquatic friends.  We’ve put together this list of symptoms to assist you with diagnosis and treatment suggestions to help you decide on the best course of action.

New pond keepers may find it useful to know that the health of your fish relies greatly on the quality of your pond water. It is advisable to test your water regularly and treat it accordingly. The water can be routinely treated with PondXpert Pond Tonic Salt and Blagdon Stress Away (formerly General Tonic) which will also help to combat any diseases. The salt helps to boost the fishes immune system which allows them to be able to cope with diseases themselves.  The level of salt which should be added changes according to the reason for usage.  It is important not to put too much salt in the pond in as this can do harm to the fish.  A good example would be cold water fish being placed in sea water and the effect it would take. A rough guide can be seen below.  Once the salt has been added it will remain in the water indefinitely unless removed via some method of water change.






455g per 455 Litres (100 Gallons) or 1tsp per gallon

pH Buffer


455g per 455 Litres (100 Gallons) or 1tsp per gallon



1.365kg per 455 Litres (100 Gallons) or 1tsp per gallon



4.095kg per 455 Litres (100 Gallons) or 1tsp per gallon*

We would always recommend testing your water with either the Blagdon Pond Health Test Kit or the Tetra Pond Test 6-in-1. These testing kits will be able to identify any chemical problems in the water; particularly pH, Ammonia, Nitrites and Nitrates. Further to this, the Blagdon All-in-One Fish Treatment will help to treat problems with parasites, fungal and bacterial infections, white spot and fin rot. We would also recommend that you look at how much Oxygen your pond is getting; our blog post on this can go into the aeration in greater detail, but an aerated pond will help to reduce the levels of infections.

Fish Diseases

 You may also find the image below helpful for being able to identify various symptoms.

Unexplained Death of a Fish

If you have tested the quality of your water and examined the dead fish for any potential symptoms for the cause of death, but are still searching for answers, there are a number of possibilities that could have caused a sudden death.

  1. Old age
  2. Unexpected water pollutants can affect ponds quickly such as pesticides and gardening chemicals.
  3. De-oxygenation can affect larger fish as they have larger oxygen requirements. Hot weather can affect this
  4. An Acute systemic bacterial infection can affect a fish so rapidly that symptoms don’t have time to show.

In addition to the above table, we have provided various images of the diseases below.


Disease Symptom Image Treatment

Mouth Fungus

Cotton wool-like growths on the Mouth
Cotton wool like growth symptoms around the mouth of the pond fish

Anti-Fungus & Bacteria


All-in-One Fish Treatment.

Pop Eye

Cloudy eyes / Bulging eyes Pop eye in goldfish: Why your goldfish has big swollen eyes


Anti-Fungus & Bacteria

All-in-One Fish Treatment

Carp Pox Shiny cotton wool growth Shiny Growth on Ponf Fish displaying Carp Pox

Ensure good water quality.

Test the pond water with the Tetra Pond Test 6-in-1 or Blagdon Pond Health Test Kit.

Anchor Worm Sharp spines sticking out of the Fish Sharp Spines sticking out of fish fins Anti-Parasite
Costia Grey sheen on body - Cotton wool-like strands Grey Sheen on body with cotton wool like strands on Fish Anti-Fungus & Bacteria. Difficult to Treat Effectively

Tiny white spots all over the fish. 

Caused by poor water quality; fish are also suceptible to this when stressed

Tiny white spots all over fish


All-in-One Fish Treatment

Fish Lice Small disk shaped creatures crawling all over the Fish's body. Small disk shaped creatures crawling on the fish Anti-Parasite

Skin/Gill irritability

Fish scratching, scraping or flicking against things

Red sore patches on body

Body Flukes Fish Disease – Tropical Fish Site

Anti-Ulcer and Parasite


Bloated body

Scales sticking out

Pond fish with bloated body and scales sticking out

Anti-Fungus & Bacteria


Leeches Elongated brown/black worm protruding from the Fish Elongated brown or black worms on fish


Clean out pond to eliminate leech

Intestinal Worms White skin lesions (rot)

Anti–Fungus & Bacteria

Stop feeding until cured

Add Oxygen to the pond




Gold/grey spots

Increased respiratory rate

Marine Velvet - Fish Disease Information - Algae, Disease, & Pest ... Anti-Parasite
Fish Ulcer Ulcers / open wounds Bacterial infection of fish with ulcers/ open wounds Anti-Ulcer

As always if you require any further assistance then please contact us.

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