Guppy With Large White Swollen Patch Of Skin

[MarieGuppy]

Hello!
I have brought home a few new guppies a couple of days ago and one of them is displaying a large patch of white skin. The white stain covers part of his head and side, as well as a pectoral fin. His other pectoral fin is transparent and healthy.
The guppy is not displaying any strange behaviour and is eating and swimming normally.
I am worried that it may be a fungus or bacteria.
Can someone please help me identify what the matter is? Your advice is very welcome.
Here is some more info:
Tank size: 100L (=26 US gallons)
pH: 7.3nitrite: 0
nitrate: 0 to 5
kH: 12 to 15
gH: 8
tank temp: 23.5 Celcius (74 F)
Volume and Frequency of water changes: I do a 20% water change weekly
Chemical Additives or Media in your tank: I add some QuickStart bacteria and water conditioner at every water change, and i follow the manufacturer's instructions
Tank inhabitants: only male guppies. There are 26 of them which is, i believe, the maximum I can accommodate in a tank that size.
Recent additions to your tank (living or decoration): I recently brought 16 guppies. I had 10 previously. The tank has fresh water plants but none of them have recently been added.
Digital photo (include if possible): I have added a photo. It is somewhat blurry but it gives you an idea.

Thank you very much for your feedback!!

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[PrairieSunflower]

Is the patch fuzzy in appearance? If so could be fungus.

 

[MarieGuppy]

The white patch is not cotton like. I just noticed that another of the new fish i got recently is also showing some white coloration on one of his pectoral fins...

 

[PrairieSunflower]

Maybe read about collumnaris (hope I spelled that correctly) and see if that matches the fishes symptoms. I've not had that or treated that before.

 

[MarieGuppy]

Thank you! It looks like we got our culprit. I will take measures immediately and go to the aquarium store tomorrow morning as soon as it's open.
Thank you very much for your help! Much appreciated!

 

[PrairieSunflower]

Hope your fish recover! I think our best fish experts are away for the holidays, usually there are more responses to problems.

If you need to know more, I am sure you could search this forum and skim for stuff that Wilder has said about collumnaris.

 

[MarieGuppy]

Hello!
I spoke to the man at the aquarium/fish store and showed him the photos i took. He was absolutely sure that it was fungus. He said that with guppies, because they have quite a tough skin, the fungus may not look cotton like but still is fungus. I'm going to go with it and hope he's right.
I have done a partial water change today and i've removed the carbon filter and increased the temperature of a couple of degrees as he instructed. I really hope the anti-fungal treatment will work...
For the moment the fish are all lively and behaving as usual, although in a newly green funky water! Fingers crossed!

Thank you very much for your help, i'll keep you posted!

 

[MarieGuppy]

Well, after 4 days of anti fungal treatment, I saw no improvement so I decided to try something else. I isolated the fish in a separate tank and gave him some broad spectrum antibiotics. Unfortunately, he died this morning.
The good thing is that none of my other fish display any symptoms (I had some doubt about one of them but it turned out to be ok).
Thank you for your help though!

 

[PrairieSunflower]

Sorry to hear that.

I have one guppy that gets fungus from time to time and it has always been fuzzy. Usually there is a noticeable difference after the first two days of treatment.

Hopefully whatever the issue was hasn't spread to any other fish. Keep the water nice and clean and that should help and hopefully protect the others.