Molly Swimming Terribly! Please help!

[Cataclysm-cat]

I have a dalmatian molly that I purchased four days ago and had issues from the start. After introducing her, along with four other mollies and fourteen guppies, I realized two days afterwards (after three guppies were found dead) that some of the guppies had cottonmouth. I purchased Melafix and added it about six hours before the molly started swimming strangely. She is rolling at the bottom of the tank, wobbling while swimming, laying on her side, and bumping into rocks and plants. I thought it might be swimming bladder disease, but I haven't seen a fish with it act this way. I have many years of experience with fish tanks but have never owned mollies and have never had any serious problems with any diseases until I purchased these fish. Please help! Tank specs below.

All levels are normal (PH, NO2, NO3, KH, GH, Amonia...etc...)
Levels were tested before and a few hours after Melafix
Water changes are 30% ever six days
75 gallon tank
Fish in tank currently include: Five Mollies, eleven guppies, five ghost catfish (around four years old)
Live plants
I also added Aquarium salt when I saw signs of cottonmouth two days ago
I feed them a wide variety of food including: brine shrimp, blood worms, and fish flakes..no food stays in the tank after feeding
Also, this tank has cycled for three months before adding any fish and given a boost of "quick start" right after setup

 

[Byron]

Welcome to TFF.

We will need more data to help. When you say "all levels are normal," we need to know what exactly they are. I am particularly interested in the GH, KH and pH, but ammonia, nitrite and nitrate are also critical here. Providing the numbers for these tests may show us the problem, or if not, remove the possibilities of it being one of these.

Second, salt is not good for freshwater fish. It is sometimes the best treatment for specific issues, but as an additive on a regular continual basis, no. Mollies can tolerate it better than most fish, but your "ghost catfish" cannot.

I doubt fish would die so quickly from true cottonmouth (I will assume this is the bacterial issue often mistakenly thought to be fungus) and it may more likely be something else entirely; adding Melafix may have worsened things. These "catch all" remedies rarely do anything beneficial, and as every substance added to the tank water will be inside the fish, sometimes if not always the substances add stress which weakens fish further.

I would suggest a major water change to get the Melafix and salt reduced. Knowing the numbers for the tests will certainly help us.

Byron.