I'm also in Florida and have been researching this in preparation for the chicks I'll receive in a few weeks. I ordered from Sand Hill Preservation, but I found this info at Cackle Hatchery,
"Jeff Smith of Cackle Hatchery additionally recommends adding 2 tablespoons of apple cider vinegar to each quart of the chicks’ drinking water for the first week. In Jeff’s experience, the vinegar greatly reduces the possibility chicks will suffer from the common disorder pasty butt."
I've read everything from 1/3 cup per quart for treatment of coccidiosis to as little as 1/4 tsp per gallon (for adult chickens). I realize the question has been asked a million times, but I would like to use it for my chickens as I already drink a little myself (Braggs) so we always have it around anyways.
So maybe I'll ask the question a different way. How much Braggs UACV is too much per gallon if you plan to use it on an ongoing basis, for baby chicks and adult chickens (if there is any difference) considering the heat in a FL summer, etc.
To SJ and D57, I can't answer your question with any authority, but I'll tell you what I do, and then throw a ? back at you for your perusal.
I would offer the birds a choice. Plain water, and an other container of water with ACV. This way, they get to choose which one to drink, and I'm guessing they will drink which ever water happens to meet their metabolic needs at the time.
I use fermented feed, which has the bonus of having plenty of moisture in it. It is loaded with probiotics, and is much easier for the birds to digest, resulting in savings on my feed bill, and their poop is not as smelly.
The pH of FF is also lower. My understanding is that the lower pH helps to keep their guts healthy and to ward off internal parasites.
Now, here's my ? for you thinkers:
If gator Ade, and other electrolyte solutions have a HIGHER pH than water (you put baking soda in home made electrolyte or gator ade)...
Then, why are we being urged to put ACV into the bird's drinking water on a hot summer day, or for that matter, on any day, when they are eating dry feed?
If you are using dry feed, ACV does serve a benefit in the probiotic and perhaps the acid benefit it provides. But, I would caution against using it as THE ONLY source of drinking water. Perhaps you might want to do a little experiment: set up 3 identical bowls of water: one plain, one mixed with electrolyte solution (omit the flavoring) and one with ACV. See which bowl has been used the most by the end of the day. See if there is any particular time of the day when one bowl is favored over the other?
The old timers used to make a drink called Switchel:
https://en.wikipedia.org/wiki/Switchel
This was a sweetened drink with vinegar added. Often used by the farmers as they were bringing in the hay.
Now, my ?
Did this acid drink satisfy as well as, or better than the basic gator ade that is used today? Which balances the electrolytes of the body more, thus being more healthy especially in times of stress or high heat exposure? 
2 tbsp of ACV/quart seems like a LOT. Part of this is based upon the lower water consumption that a chick versus a chicken will have. Just like some vitamins if you read the package put a much higher concentration of the powder in the chick water than in the adult chicken water.... I'm sure that Jeff Smith of cackle hatchery is on to something. Perhaps the chicks will drink more water when vinegar is added. Conventional wisdom I've heard says: "make sure the chicks are drinking water before introducing any feed, as one way to prevent pasty butt." Another excellent product is the green gel called 'gro gel'. putting even a pinch in the brooder water seems to help the chicks. Shippers sometimes make it into a goo and include it in the shipping box.
