You can mix a whole gallon and store the excess in the fridge or just mix up a quart or 1/2 gallon at time...depends on your water station I suppose.
I would probably change the water a couple of times a day if possible. I would put out "fresh" at least once a day.
It's good practice to...
How do the chicks act?
It does look like it may be intestinal shed, but I would monitor them for any symptoms of lethargy, not eating/drinking, puffed up appearance. If you notice more like that, then it won't hurt to treat with Corid.
Dose for Liquid Corid is 2 teaspoons per gallon of...