Is this a new tank? Meaning newly set up? Then it could be that the tank hasn't cycled yet, so ammonia is not being efficiently removed.

Sometimes a water change can help.

Also - swords do need salt in the water.

i have let it cycled already. what brand of salt do you recogmend and where can i get it? I think i will also do a water change. Thanks for your help!

You need to use Aquarium salt... found in the fish section. That or NON-iodized salt. Don't use regular table salt with iodine.

See the link below inre more info on Brackish water fish and fishkeeping!

Here is a link that might be useful: Brackish water faqs

Well, you can try a little salt. It can serve as a cure in some cases for certain diseases, but...swordtails don't need salt on a regular basis, and your swordtail may or may not actually have a disease. But as a stop-gap, it can't hurt (just don't add too much!).

I have kept and bred swordtails, and find that they do just fine in pure fresh water. Their native habitat is water that is relatively hard and alkaline, so of course they prefer that sort of water. If your tap water is very soft, the fish may not adapt well to it. You can add some African cichlid salts to your water to harden it up a bit, if this is the case.

Thank you so much for all your suggestions i will try them ASAP. I'll let you guys know when she gets better!

Swordtails can be agressive toward each other. One may just be submissive. Does it compete for food with the other two?

occasoinally, the male kinda pushes her down but she gets the food that falls

Hello. I am sorry to announce but the female with the fin problem has died today(4-7-05). I would still like to know how it happened.