Puffy white tail lesion tetra. Multiple neon loss

[Pitafish]

I recently added some amano shrimp to the tank for algae clean up.  A week passed and now multiple neons are missing and one did get pulled by filter intake.  Could not see evidence of disease until today.  
my fancy tetra as a white lesion (doesn’t look like ich).   I was going to treat with kanaplex but would it harm my plants or invertebrates?    I can do a hospital but not quickly.   
I don’t want to loose anymore!

thank you 

Parameters good.    I can do hardness if needed.  

[Colu]

What exactly are your ammonia nitrite nitrate and are they eating ok any rapid breathing hanging near the surface sitting on the bottom of the tank  

[Pitafish]

Ammonia zero, nitrite zero and nitrate 40 (I use the co-cop fertilizer.  Everyone is eating well except the

 

 

well crap.  Ammonia is high.   Doing water change.  I’ve been feeding too much likely.   

[Pitafish]

No ammonia today after a 50% water change and cleaned one of my three filters.   
 

The tetras are all eating and doing well. Everyone is very active.  
 

but tonight I noticed a cory not active at the bottom.  Feed and everyone eating but this Cory.  Use pelafix yesterday maybe 30 minutes before my water change.   Just reading it can hurt their lungs.  
I have two other tanks I can move them to.   (I have five Cory’s)

not sure what is happening.   Everything was great until I added some amano shrimp and nerite snails from aqua huna.   
 

my Cory’s are my favorite and if I’ve killed them …..I’m throwing in the towel.
 

looking at him, he does seem a bit smaller than the others but he’s been fairly stationary for past hr.  
 

ammonia 0

nitrate 20

nitrite 0

pH low 7.6

pH high kit maybe 8.2

my water is soft from a softener.   Chlorine is 0 but I still add prime   
 

I was hoping it would fix issues without having to move any fish.   I usually look up things before I use them but just checked if it was okay for my shrimp and snails.   
 

any help appreciated.   
 

H
 

 

 

 

 

[Colu]

PIMAFIX won't harm your Cory's its more like a mild antiseptic treatment I would add an extra air stone as PIMAFIX is a plant oil based treatment that will lower your levels of desloved oxygen and add a small amount of aquarium salt 1 table for 5 gallon that will aid Gill function and add essential electrolytes and at that level it shouldn't harm your plants