i posted this in another channel, but i guess this one is more appropriate...

i recently put some new fish in an old 50 gal tan,k that a 17" pleco, and 2 little tetras were habitating. i recently shocked my tank with some marycyn before some newbies went in (a couple of angelfish, some scissor tails, danios and tetras), but a few died over night. i then realized that i had purchased salt-water, not fresh water marycyn..
i have a freshwater tank.
do i need to drain the tank? will the saltwater marycyn kill my fish, or is it benign. as far as i can tell, the saltwater antibiotic only has extra B vitamins in it.
anyone?\
.. more are dying as i type.

your help and advice is appreciated.

/sorry to 2x post.

See my other post.

double posting this to make sure it doesn't get burried...

one of the most distinctive signs of fish TB, a bacterial infection, is an S shaped or bent spine. Check out these articles on fish tb. http://www.4qd.org/Aqua/disease/tb.html and http://www.4qd.org/Aqua/disease/tb.html#symptoms Spinal deformities is listed as a symptom of both, along with protruding eyes.

As for whether the medicine is toxid or not, you said it was the new fish that died. How did you go about aclimating them? My guess is something went wrong here. However, the general rule is if you have sick fish, don't add new ones for two weeks after the last death. With fish TB, you want to wait longer to make sure none others have the disease but aren't showing symptoms yet.

If you are worried about the med (i couldn't find any info on it), do a partial water change and add some carbon to the filter.

And finally, what are your water stats? This this is always one of the first things you should check when something goes wrong in your tank.