Your tank is overcrowded and you have a fungus that will continue to kill your minnows. You have too much aeration and too much turbulence in the tank which is causing stress on your shiners. You need to add around 4 ounces of rock salt and 2 tablespoons of oxytetracycline,which is available at your local coop, to the tank. The antibiotic will kill the fungus and the rock salt will promote the slime layer. At best, the tank should only hold 1 pound of minnows and the minnows need to be fed.