I wouldn't keep them on that electrolyte probiotic water more than a few days. I think that can help contribute to pasty butt. I would also make sure the crumbles you feed them are "FINE". Some chick starters are actually kind of large crumbles for three day old chicks. I don't want to name names, but one well known brand is like this and I have to get the rolling pin out every time and break this stuff down to a finer crumble during the first week.
And if it was me, I would have a bottle of NutriDrench on hand if I'm expecting shipped chicks. I think a few drops of that in their beak would help them perk up better than anything else out there.
Oh, and I wouldn't think chicks that you just got and haven't been on any "ground" would pick up cocci so quick. I never have to worry about my chicks as long as they are in the brooder. It's when they hit the ground, that's when you have to do a preventative.