One sick Molly?

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Mollyfishes4

Aquarium Advice Newbie
Joined
May 21, 2023
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I have a 30 gallon tank that houses 6 mollies. They get their water changed and gravel vacuumed once a week. This morning I noticed that one Molly has a torn, shredded back fin. I can't tell if it's fin rot or from bullying. It seemed to have appeared overnight. Everyone else looks perfectly fine. I don't have my parameters right now. I plan to take some water for testing later. Any ideas?
 

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Hi and welcome to the forum :)

It looks like physical damage. Check the tank to make sure there is nowhere for the fish to get caught in, on or under.

Wipe the inside of the glass down with a clean fish sponge. This removes the biofilm on the glass and the biofilm will contain lots of harmful bacteria, fungus, protozoans and various other microscopic life forms.

Do a 75% water change and gravel clean the substrate. The water change and gravel cleaning will reduce the number of disease organisms in the water and provide a cleaner environment for the fish to recover in. It also removes a lot of the gunk and this means any medication can work on treating the fish instead of being wasted killing the pathogens in the gunk.
Make sure any new water is free of chlorine/ chloramine before it is added to the tank.

Clean the filter if it hasn't been done in the last 2 weeks. However, if the filter is less than 6 weeks old, do not clean it. Wash the filter materials/ media in a bucket of tank water and re-use the media. Tip the bucket of dirty water on the garden/ lawn. Cleaning the filter means less gunk and cleaner water with fewer pathogens so any medication (if needed) will work more effectively on the fish.

If there's not a lot of aeration, then increase surface turbulence/ aeration to maximise the dissolved oxygen in the water.

Add some salt, (see directions below).

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SALT
You can add rock salt (often sold as aquarium salt), swimming pool salt, or any non iodised salt (sodium chloride) to the aquarium at the dose rate of 1 heaped tablespoon per 20 litres (5 gallons) of water.

Keep the salt level like this for 2 weeks.

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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