Help! Unidentified disease on guppy

[Darkomot]

Hello! I got a few guppies from my local fish store a few days ago and had to add them to my main fish tank without quarantining them because I can't afford a quarantine tank. Sure enough...just a few days after one of the guppies quickly developed this odd disease and symptoms. The back half of the fish had become cloudy and it appears that the guppy's tail was paralyzed, and the tail has lost most of its color and seems to have rotted off in one day!! Just two days ago the fish had no visible issues that I could see. What could this be, and how should I deal with it so that the other guppies in the tank stay as safe as possible? Update: I had to euthanize the fish in this picture, and now another female guppy has also developed similar but less aggressive symptoms. What do I do??? FYI: I have added salt to around .7 tablespoons per gallon to help (I still don't know what this is) Thanks!

 

[Darkomot]

@Colin_T

 

[Colin_T]

bad bacterial infection.

add salt and a broad spectrum fish medication that treats bacteria, fungus and protozoan infections.

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You can add rock salt (often sold as aquarium salt), sea salt or swimming pool salt to the aquarium at the dose rate of 2 heaped tablespoon per 20 litres of water.

If you only have livebearers (guppies, platies, swordtails, mollies), goldfish or rainbowfish in the tank you can double that dose rate, so you would add 4 heaped tablespoons 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, 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 but the higher dose rate (4 heaped tablespoons per 20 litres) will affect some plants and some snails. The lower dose rate will not affect 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.