API Pimafix, Melafix, and EM Erythromycin - Anything Else to Rid Tank of Whatever Has Killed Many of My Fish? Fin Rot.

[Scraig325]

We recently lost an albino cory catfish, a white molly, and a danio in my 55 gallon freshwater tank (their bodies had some lesions and red lines on them) I thought my ghost shrimp were attacking them and eating them since I found the shrimp eating their dead bodies. I had my water tested at the local pet store and they said my water levels/readings were all really good. I noticed one of my black skirt tetras had a white dot on its nose so I assumed I should treat for ick, which I did. Then I noticed the same fish was losing its back tail, and a neon tetra was missing its top lip. I started the next day with API Pimafix and Melafix. Its tail was still rapidly disappearing next day (fin rot), so I added EM Erythromycin to the treatment. The neon tetra died and so did my black skirt tetra (the fish basically dissolved into nothing).  Now I'm going to complete the 7 day treatment with Pimafix, Melafix, and 4 day treatment of EM Erythromycin to ensure all the other fish are ok. My question is, do these medicines rid the entire tank (gravel, decor, live plants, water) of fungus, bacteria, whatever disease is in there? Or do those only treat living fish bodies? Do I need to use a parasite treatment or other medicine? How soon should I wait to introduce new fish?  I had all those other fish for 6 weeks +, but added some small neon tetras a week prior to the few that died (assuming they were carrying a disease even though none of the new guys died). The only other thing that's different is I started feeding my fish freeze dried blood worms, could those possibly carry disease?  Pic attached, sick tetra on left, "healthy" on right.

Edited October 30, 2020 by Scraig325
added photo

[Irene]

Sorry to hear about all your troubles! I bet the neon tetras probably brought the disease in. From the symptoms that you describe, my first guess would be that it's some kind of fast-acting bacterial infection like columnaris. Some fish may be too far gone to save, but I would complete the erythromycin treatment. If the erythromycin doesn't work, you could try using a strong concentration to salt to treat them in a separate hospital tank. (Salt is bad for live plants, so don't put salt in your main tank if it has plants.)

1) Here is an article on how to treat sick fish (and how to quarantine any new fish to prevent diseases from spreading):

How to Treat Sick Aquarium Fish (Even If You’re Not Sure What’s Wrong)

WWW.AQUARIUMCOOP.COM

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Treating sick aquarium fish can be difficult, especially if you’re new to the hobby or have never seen this disease before. Based on years of experience helping customers at our fish store and online, here are the step-by-step...

2) Here is an article on how to use aquarium salt to treat diseases:

Aquarium Salt: When and How to Use It Properly

WWW.AQUARIUMCOOP.COM

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Should aquarium salt be used in freshwater tanks? Some people recommend dosing it all the time to provide fish with essential electrolytes while others say it’s mostly used for treating diseases. After years of testing with...

Hope it helps, and let us know what happens.

[Cory]

I'd also make sure you have a test kit and can look at the parameters yourself. There could be bigger things going on here but without water parameters and maybe some info about your tank and some more wide shot pictures it may be hard to identify.