I have been noticing a problem I have with minnow...I caught some last few months ago...some shiners...stonerollers...top minnows....and many of them died of a disease or something...that began at the tail...for example...the tail will start to look whitish...like the flesh is dead or something...and it starts to spread towards the rest of the body...turning pale...then the fish starts to struggle like the other half of its body is paralyzed...I have attached a photo of a top minnow with this problem...

I have been noticing a problem I have with minnow...I caught some last few months ago...some shiners...stonerollers...top minnows....and many of them died of a disease or something...that began at the tail...for example...the tail will start to look whitish...like the flesh is dead or something...and it starts to spread towards the rest of the body...turning pale...then the fish starts to struggle like the other half of its body is paralyzed...I have attached a photo of a top minnow with this problem...

It's an opportunistic infection by an amoeba-like organism usually found in low levels in the gills. When fish are stressed by capture and transport, especially in warm water, these amoeboids can grow very quickly especially on fins. In my experience it's fatal sooner than later. The one thing you could try is a 30 minute saltwater dip, on the theory that the fish has a better osmoregulatory system than one-celled organisms.

Sadly moments after the fish died....one minute I saw him struggling...the other he was on the bottom and my crayfish had started dining on it!
The other two minnows are ok...healthy...but I noticed also my Tinfoil barb in the tank the top fork of its tail has some damage...like its been bitten off and whitish...but I dont have any other fish in the tank...so I am worried he might get it too...
Can Kosher salt work for a saltwater dip? kosher salt is pretty much sea salt with nothing in it....also the for the dip...if I have one gallon of water how much salt should I put in?...I might also add a couple teaspoons to my 29 gal tank...but theres 2 crayfish in it...and the salt is harmful to the crayfish?

Sadly moments after the fish died....one minute I saw him struggling...the other he was on the bottom and my crayfish had started dining on it!
The other two minnows are ok...healthy...but I noticed also my Tinfoil barb in the tank the top fork of its tail has some damage...like its been bitten off and whitish...but I dont have any other fish in the tank...so I am worried he might get it too...
Can Kosher salt work for a saltwater dip? kosher salt is pretty much sea salt with nothing in it....also the for the dip...if I have one gallon of water how much salt should I put in?...I might also add a couple teaspoons to my 29 gal tank...but theres 2 crayfish in it...and the salt is harmful to the crayfish?

Try about 3-4 tsp of salt per gallon as a very rough approximation, and Kosher salt should work fine. If you add salt to your big tank, dissolve it in some water and let it sit for 24 hours before adding it to the tank; freshly dissolved salt is "aggressive", not fully in solution. I'd think that crayfish could tolerate 2 tsp in a 29 gal tank.