mollies swimming virtical

Question
its totally bizare, the fish is eating normally, swims to the bottom to get food can right for short periods and now has started to swim under the filter with its tail held down by the filter to rest the right way up. it is still very active dispute the virtical swimming. nothing wrong with the scales. heres a photo of him (i now think its a him) http://www.digital-criminals.co.uk/molly.JPG . Thanks again for all your help
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Thanks for the fast response. I am not sure how to sex a molly, any tips would be good. If it is in labour how long will it stay like this before we see the fry? I have not added salt because of the phantom tetra,i hear thy are totaly intoterant to salt. Also the plants i have been told will die in brackish water. I have a hospital tank of 14L should i convert this to a brackish tank and move them in there? Thanks again for your help
Gary
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I have the same problem as another reader, one of my Mollies is now swimming vertically and has a slitly pot belly. He spends most time at the top of the tank with his tail on the surface this way it can almost right itself. the other molly often swims very close.
Any ideas?

tanks is a month old.
water is pH 7, 0 ammonia, 0 nitrite, 0 nitrate tanks is 2' x 1' x 1'
tankmates 2 dwarf gouramis, 3 clown loaches,a bristel nose catfish, a betta and 8 phantom tetra.
plants: amazon sword leaf, Hygrophila polysperma, Hydrocotyle verticillata, Limnophila sessilifora.
thanks Gary
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Your fish with a pot belly, do you know for sure it is a male as you did not indicate if you are aware of how to sex a molly. If it is a male and having this problem it sounds like it most likely is a swim bladder problem. There is medication for it but usually only prolongs life. If it is a female she could be pregnant and in labor. Mollies in general with other live bearers prefer a little aquarium salt in their tank. They really thrive when this is provided. Best of luck and happy fish keeping.
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Regular aquarium salt will not create brackish water, regular aquarium salt will filter out of the tank. Sea salt is what is used to create true brackish water. When working in fish retail I never had any loss with tetra when I salted the tanks using regular aquarium salt. Your plants may not appreciate it though. You don't need to set up a hospital tank, if anything consider adding a small amount of regular salt which simplies adds minerals livebearers thrive in. To sex a molly look at their anal fin, a females will have her anal fin spread out like a normal fin and male anal fin will appear crunched together and not fanned out. Time length on pregnancies vary with each fish, very difficult to tell on a black molly because you can not see the base of the abdoment darkening which indicates they are close to giving birth. Best of luck and happy fish keeping.

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You are correct your molly in the photo is a male, which from what is occuring is most likely swim bladder problem as this effects there ability to swim normally. The medication out there for it I have only seen prolong life. If he is sticking to your filter intake pipe he is to weak to swim away which is not a good sign. I wish I could tell you yes there is a medication to cure it but that is not the case. Best of luck and happy fish keeping!!