Urgent advise - help!!

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Sep 25, 2022
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Hi, I have a 70L fresh water tank. I have 2 koris and started with about 6 female guppies and 4 male guppies. I’ve had them for about 7 months and it was going well. They have been procreating and I think I ended up with about 25 guppies or so. I went to my usual fish shop yesterday and they recommended getting a couple new guppies so the population doesn’t get too inbred. I bought 2 new females and 2 new males.
Now comes to the problem. This evening I came home to find 12 of my guppies dead. Including all 4 of the fish I bought yesterday lot of the dead fishes tails had gone clear.
I checked the water (I have the API home test kit) the PH, ammonia, nitrite and nitrate are all seemingly fine. The only thing that might be a bit off is the nitrate is about 10-20ppm.
I did a water change but can see some of my remaining guppies tails are also going clear. There’s also one guppie floating vertically sinking to the bottom then shooting up to the top and repeating this pattern.
The photo attached is of one of the remaining fish whose tail is going clear, it used to be big, bright and yellow.

Any advise would be greatly appreciated. Please be kind I’m still a relatively new fish mum.


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Sadly, you have brought in a disease from the shop. It's why we all suggest quarantining new arrivals for several weeks in a second tank (and very few of us do it because of a second tank). Is it viral? Bacterial? How do you know? It's fatal.

I have had fish for 50+ years, and I can't identify that one. It came in the new fish. I doubt any med you can buy will do much, as you'd be guessing. i doubt the store knew their fish had it, although it's like they should be quarantinng better to give it time to see if the stock they received from the wholesaler was healthy.

Keep the water changes regular, remove the dead quickly and ride it out. I can't think of one thing you can do that wouldn't just be something to make you feel like you were helping the fish.
Since the fish died so fast and is having frayed tail, it could be Columnaris (bacteria) infection especially for Guppies(live bearer).
This disease will kill very fast and you have to treat it as soon as possible.

Use API Furan-2 (Nitrofurazone) and Seachem Kanaplex (Kanamycin). These are anti-biotics.
Wear gloves whenever you use any medications.

Treat the whole tank for 7-10days.
Any net or anything that is in touch with the water of the tank need to be sterilized with hot water or bleach.

Also, slowly reduce your water temperature to about 23C as bacteria grow faster in warm water.

But most importantly, you have to use the medications as cooler water won't kill them. It only slower their activity.

Take note that the antiobiotics will also kill of your beneficial bacteria.
So, your tank filter will need to restart again.
Get some live bacteria such as API Quick Start, Tetra SafeStart, etc after the treatment to boost the beneficial bacteria in your filters.

Lastly, as Gary mentioned above remember to quarantine all your new fish to avoid the disease from being spread to other fish.

Here are more details information.

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I looks like the fish have a couple of diseases. The face/ head is inflamed and there is a bit of white on the top lip, which would indicate mouth fungus (Columnaris). The white stuff on the tail is interesting.

Not sure if you will be able to get antibiotics but see what the local pet shop has. And add some salt asap.

You can add rock salt (often sold as aquarium salt) or swimming pool salt, or any non iodised salt to the aquarium at the dose rate of 2 heaped tablespoons of salt per 20 litres.

Keep the salt level like this for at least 2 weeks but no longer than 4 weeks otherwise kidney damage can occur. Kidney damage is more likely to occur in fish from soft water (tetras, Corydoras, angelfish, Bettas & gouramis, loaches) that are exposed to high levels of salt for an extended period of time, and is not an issue with livebearers, rainbowfish or other salt tolerant species.

The salt will not affect the beneficial filter bacteria, fish, plants, shrimp or snails.

After you use salt and the fish have recovered, you do a 10% water change each day for a week using only fresh water that has been dechlorinated. Then do a 20% water change each day for a week. Then you can do bigger water changes after that. This dilutes the salt out of the tank slowly so it doesn't harm the fish.

If you do water changes while using salt, you need to treat the new water with salt before adding it to the tank. This will keep the salt level stable in the tank and minimise stress on the fish.

When you first add salt, add the salt to a small bucket of tank water and dissolve the salt. Then slowly pour the salt water into the tank near the filter outlet. Add the salt over a couple of minutes.

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