One of my goldfish, which I've had for 3 months, suddenly got a white patch on the top and a white spot on its left side (the yellow-black one in the picture). I just noticed it today, but I'm sure it wasn't there yesterday, so it happened very quickly.

enter image description here enter image description here I just moved my fish to a new, larger, 20 gallon (76 liters) tank 10 days ago, and added a Seachem Flourite substrate, but other than that everything is still the same.

Any help is appreciated, thanks.

UPDATE: the white film on the fish seems to be spreading, I see it on its head, gills, and tailfin enter image description here

I also noticed brown spotting on its fin and from researching online apparently it might be from ammonia but I've been doing 10% water changes almost daily, and none of the other fish appear to be affected, anyway I did a 50% change today since I didn't have any water testing strips lefts just to be safe.

enter image description here

but the thing is you can only see it under a bright light, when it's not directly under the LEDs you can barely see it enter image description here enter image description here enter image description here

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    welcome to pets.SE, which of the two orange/white fish in the picture do you speak about? Commented Nov 18, 2020 at 4:38
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    @Allerleirauh I'm not question author, but I think the description matches that yellow-black fish in the right that is lined up with a heater.
    – lila
    Commented Nov 18, 2020 at 10:29
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    @Allerleirauh it is the yellow-black one as lila mentioned. I think it's spreading too, I think I see a white patch on its left gill today. I will update my post and try to get better pictures, but they're just so tiny and keep moving quickly. Commented Nov 18, 2020 at 18:05

2 Answers 2


Your fish have got a fungal infection,this is often a result of poor waterquality and when this happens there is a couple of things you have to do.

no1,Stop feeding your fish and do a watertest and look for ammonia-nitrite-ph,if the nitrite or ammonia is high you need to do a partial waterchange in your tank about 20% of the water needs to be replaced remember to treat the water before adding it to your tank.

no2,Add some aquarium salt the dosage is 0,3%,this is to block a potential nitrite poisoning and to increase the bloodflow in the skin and gills of your fish to help your fish fight the infection.

Some of the causes for poor waterquality is not cycling the tank properly(this is if your fish get ill right after you start your tank).

other problems with waterquality is often caused by overfeeding your fish or by not maintaining good waterfiltration(cleaning the filter too often is just as bad as not cleaning it at all)you need to clean the filter only when you can see that the waterflow is reduced but before the filter gets clogged up.

Remember to do weekly waterchanges and dont forget to vacuum the gravel to get rid of the waste collecting there.

If you want to medicate your fish you have to do this in a separate tank and not in your main tank,most medication will kill the good bacteria in your tank and you will have to cycle your tank again,to learn about how to cycle your tank please take a look here:https://www.fishlore.com/NitrogenCycle.htm if this link dies you can do a search for how to cycle a fishtank.


Have you added any new soils or plants or rocks or fish? That is how white spot disease spreads. It is highly contagious so I highly recommended to get medicine as fast as you can. If left too long, it will spread and may possibly kill your goldfish. Turning up the temperature will help.

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