aquarium salt and Swardtails

Question
you ask for symptoms of my dying swords ;  they would "stay out of sight" first sign, then got just sitting or resting alot on the the bottom, last didn't eat at all or jsut a sm. amount.  also the one female had some of her tail missing and her black was looking somewhat white. But, the last one that died looked perfectly normal as far as color but he also rested and hid alot before dying. Thanks for answering ,Eileen-------------------------
Followup To
Question -
My 20 gallon tank has been up and running for 14 months.  I now have a couple of Danios a male betta and one male swordtail.  I have a "hanging"  pump and filter system using the easy to change filters just slips in and out.
The ammonia tests shows perfectly clear water.
But, I do add aquarium salt once a week to about 4 gallon of fresh treated water when I do the water change.  But, anyway I have purchased 2 female swordtails and two males.  All my females have died and one male has also...also my "orginal" swordtail died --first. I am now wondering if the aquarium salt might have something to do with with all of suden sudden losing only Swordtails.

HELP....Eileen
Answer -
Hi Eileen;

Swords are really not sensitive to salt. I would expect the other fish to have trouble before the swords. What kind of symptoms do the fish have before they die?

Followups welcome

At Your Service;
Chris Robbins

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Answer
Hi Eileen;

There may be a trace mineral or some other element missing from your tank that swords need. Some tanks just can't support livebearers in general. No one knows why. Other tanks can't support plecostamus, or gouramis, or tetras. It just happens sometimes. You could try setting up a tank that has only swordtails if you really want to keep them. Or, try another fish store. Maybe the store you got them from just has weak ones.

You might want to visit the freshwater forum and ask your question there. There could be someone there with more insight on this than I have.

At Your Service;
Chris Robbins

Come on over and join us on the freshwater fish forum at About.com to get even more information too;
http://forums.about.com/ab-freshaquaria/start

My member name is ChrisR62. See You There!