I started using Braggs ACV for my 2 week old chicks to see if it would clear up runny poop from one of my 6 chicks. It worked. I use 3/4 tsp ACV per 3 c water (1/4 tsp per 1 c). Braggs simply because that's what I always buy and 3/4 tsp is hardly anything. I change the water every day (they don't drink it down). I did read that Chick Boost Probiotic is better than ACV and I just happen to have a small bag of it (that I bought months ago thinking I might need it, as a newbie chick owner). Since it comes with an 11cc scoop (10gr), I calculated out the U.S. quantity needed: 1 scoop = 2 rounded tsp per 1 gal water; 1 rnd tsp to 8 c water; 1/2 rnd tsp to 4 c water; 1/4 tsp for 2 c water.