Fish Dying!

[molver]

Hi, 

I got a molly three days ago. It was great! Really active and friendly! But the next night, I noticed a corner of its lower lip was white and swollen, and the fish was being very lethargic. 
 
I thought it might be cotton mouth, so the next morning I went to PetSmart and asked an associate for help. She also thought it might be cotton mouth and recommended I use Pimafix.
 
So I bought the medication and followed the directions: Removed my carbon filter cartridges, and put in two teaspoons of the medication. This was at about 9:30 am.

Then I headed off to school. I came back home around 6:30 and saw that my poor molly was dead (so it died on day 3).
 
Since it died, I thought there was no need to continue the medication, so I put my activated carbon filter cartridges back.
 
Today (day 4), I came home around 8:30pm, only to see my Betta fish suffering! It's lips are white, its fins are torn and disintegrating from the edges, and its scales are whitish. It no longer has shine. The poor thing is barely alive, it's just floating around. I don't think it'll make it
 
I quickly took out my filter cartridges and started medication again. I put in two teaspoons of Pimafix. 
 
My aquarium always had salt, about 4 table spoons in a 20 gallon long. I don't have any other tanks, so I can't quarantine any of my fish. 
 
I also don't have a water testing kit, so I'm not sure about water parameters. But I got my water tested 5-7 days ago at PetSmart, and the associate said my water is fine. 
 
Tank size: 20 gallon long
pH: don't know
ammonia: don't know
nitrite: don't know
nitrate: don't know
kH: don't know
gH: don't know
tank temp: 80 degrees farhenheit

Fish Symptoms: white lips, whitish scales, no shine. Just floating around barely being able to control direction. Laying pathetically on decorations. Unable to remain upright and balanced. Fins torn and frayed, appear to be disintegrating from the outside.

Volume and Frequency of water changes: 30% - 40% water change every week

Chemical Additives or Media in your tank: None, sometimes use Seachem Prime

Tank inhabitantswordtails, Mollies, Cory cats, Neon Tetras, Betta

Recent additions to your tank (living or decoration): 3 Cory cats about 9 days ago. 1 Molly 4 days ago (which died).

Exposure to chemicals: None that I know of

I included a picture. It's not very good, but I can't get a better shot at the moment.
 
I don't think any of my fish are stressed. All my fish are extremely active. My Mollies and Swordtails always eat out of my hand. My Betta did too. 
 
Please help me figure out what I should do.  There probably isn't much hope for my Betta, but I don't want anymore of my fish to die.

 

[WILDER]

Sorry for your loss. R.I.P.
 
Sounds like you have a bad case of columnaris in your tank. White edging to scales can also be columnaris.
Also disintegrating  fins 
Remove the Pimafix.
 
Maracyn Plus, with is a gram positive, and gram negative antibiotic. So is tetracycline. They might knock your water stats.
 
Also take a sample of your water to the LFS to be tested and ask them to write the readings down for you.
 
Lower tank temp
Get you some info.

  COLUMNARIS
 
The hospital tank should be heated to approx. 74 degrees. 76 and above is the ideal breeding temperature for columnaris. Though there is some dispute over lowering the temperature, my experience has been that 72 is too low for the medication to work rapidly, 76+ causes the disease to breed more rapidly than the anti-biotic can kill, and 74 is "just right." Remember to keep this temperature stable!
 
Text © Lauren Weeks 

 

[molver]

Just to be clear, you're recommending that I remove the pimafix and use Maracyn Plus instead?

 

[WILDER]

Yes. Pimafix is not that good and not all fish tolerate it to well.