what does IDEAL mean.. what is the ph, ammonia, nitrates and nitirites. What temp is your tank at?
There is a change the new ones you brought home had something and now its spreading to all the others...
If they are babies, you need to be feeding twice a day untill they get bigger, then once a day is ok. They need to vitamens from the food to grow bigger and healthy.
Add some salt and maybe some meds.. just watch the amount of meds you add. Or maybe get flake food that has meds in it already..
Do a 30 to 40% water change also before adding salt and meds....