Guppies flashing with no symptoms, but one dead guppy.

Hi there,

I've got a 55L tank Ammonia 0ppm, Nitrite 0ppm, nitrate 5ppm with 6 male guppies (now 5) and 6 pygmy cories.

I added one guppy and the 6 cories around 3 weeks ago. The guppy was thin when I got it but I just thought it was a different body shape.

After a while I saw he was flashing and now the other fish in the tank have started flashing too. Today I noticed the new guppy was very gaunt, struggling to swim and mostly pointing face up and hanging down. I decided to euthanise because he was sick for a while and I didn't know what was wrong. He also had fin rot. He had no other symptoms like ich or stringy poop.

The other guppies in the tank are flashing, but they are eating well, no physical injuries, no fin rot, nothing wrong with their poo.

I've treated them with a formaldehyde external parasite treatment which made no difference. Then big water change and currently treating with a silver anti bac treatment, still no change in flashing. I'm at a loss and desperate for some answers. Feeling extremely guilty that I didn't QT (no facility for it) and stressed at what I've introduced here.

I've attached a picture of the euthanised guppy in case it helps.

any chance of pictures and video of the remaining fish?

after you turn the tank lights off tonight, shine a torch on the fish and see if they have a yellow or gold sheen to their body. take pictures (have the flash on) if they do.

what are the ingredients in the medication you are using?

Here's a picture of them in the dark with the phone flash. It's so hard to see if they've got a gold sheen on their bodies. If they do it's not obvious and it's only around their gills, and that might just be their own colouring, I just don't know.

I'll keep trying to get a video of their behaviour but it's hard to catch the flashing/erratic swimming.

I used one medication with formaldehyde and malachite green oxidate. It's few years out of date though, might have something to do with it not working. Then I used another with silver proteinate.

Thanks for your help.

The fish in the picture look fine and free of velvet.

It could be due to gill flukes or skin flukes(parasites).

If you are using formaldehyde and malachite green, you may have to use it for a few weeks.
But you should be able to see some results (reduction of fish flashing/scratching against object) after a few hours unless your medication has lose its potency.
How long have you been treating them?

But the quickest solution as Colin used to mention is to use 2 tablespoons of salt for every 20 liters of water or 5.5 tablespoons for your 55 liter tank.
This can treat both the parasite and bacteria.
But you can only treat them with salt for 2-3 weeks and not longer as the some fish especially the South American softwater fish cannot withstand the salt for too long.
I'm not sure whether your Corydoras can withstand the salt, else you may have to reduce the dosage but too much reduction won't be effective to kill the parasites.

But take note that to treat gill flukes or skin flukes, you may need at least 1 month to 1.5 month. Sometimes it may take even longer.
Gill and skin flukes infection usually don't have much symptoms other than fish scratching/flashing against the objects.
At final stages of gill flukes infection, the fish will breathe fast/heavily and it can be hard to cure at this stage.

So, after treating with salt for 2-3 weeks, you may have to get ready some medications.
You can use Praziquantel or the combo of Formaldehyde and Malachite green.
Take note also that all these medications are toxic. So, wear gloves and don't breathe in the fume when you dose your tank.

Make a large water change of at least 70% to reduce the numbers of parasites, bacteria in the tank before you start medication.
Also, the medication will be more effective in cleaner water.

Thank you so much for that comprehensive advice. I'm concerned about the salt with the cories because I've read that that can affect them. There are also live plants in the tank. I only did two doses of the formaldehyde because that's what the dosage said, but I think I'll do a big water change and then consistently dose with that medication. Around 24hrs before the guppy was euthanised he started respiring heavily at the top of the tank so that probably fits with gill flukes? I did a 50% change yesterday but I'll do a bit more today and go for it again.

Thank you for your advice!

You did the right thing by removing the guppy else it will spread even more.
I realized that I need to mention a few things here.

Formaldehyde + Malachite green may kill some plants and with plants around, I am afraid that the plants may absorb the medications and reduce its effectiveness.
And if I can remember correctly, Corydoras might be sensitive to this medication according to some research papers.
Continue to observe them during treatment.
Take note that Formalin is the same as Formaldehyde.

In the past, I used to keep Corydoras but after finding out their sensitivity to most medications, I stopped keeping them.
Actually all catfish (or fish without scales) are sensitive to most medications.
But I also read about someone who had experience that Corydoras are fine with salt though the person didn't mention the level of salt that he used.

Praziquantel might be a better choice than Formalin and Malachite Green as its safer for the Corydoras and plants.

However, I find that the Praziquantel was effective for treatment against Gill/skin flukes at the beginning but after a few treatments, I stopped using the medication.
And when the gill flukes returned, the Praziquantel becomes ineffective any more.
I had to change to Formalin + Malachite Green. The same things happened with this combo.
I treated my tanks for months and I even changed tanks, filters and everything.

From all these experience, I realized that the flukes will become resistant to the medications if you don't kill them completely.
And the next round when they returned, some fish will die again until you can reduce the flukes population to very low.
The problem with gill flukes is they attack the fish gills and the wound will cause bacteria infection which will eventually suffocate and kill the fish.

Now finally, I found Flubendazole to be effective. I treated my tanks for two months and I have not seen any more symptoms of gill flukes.
I searched many websites for treatment of gill flukes and the gill flukes can stay dormant for some time before they come back.
When the gill flukes are in eggs/cysts form, there is no medication that can kill them.
The medication can only kill them when they are in swimming form.

You can try this medication called Wormer Plus which main ingredient is Flubendazole.

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