How much Apple Cider Vinegar?

I rarely use it any more but a teaspoon to a tablespoon for that size container. It is an inexact science.
If it isn't raw or organic, it won't do much but acidify the water helping to keep the slime down.
If it is raw, it adds beneficial enzymes.

 

I was told one teaspoon per gallon.

 

Also you should have it in a plastic container, not a metal container. The apple cider doesn't react well with the galvanized steel so be sure you are using PVC or plastic drinking containers when you use ACV. Hope this helps.

 

I know they say not to use it with metal containers but what about chicken nipple there is metal in those would it be corrosive on them causing them to leak?

 

All of the nipples I've seen are stainless steel components so that won't be a problem.
Galvanized and raw steel will be eaten up by the acidity.

 

Recommendations are for 1-2 TBSP per gallon. 2.5 L would be about 3/4 of a gallon, so 1 TBSP should suffice

 

I've read many different things ACV is supposed to do. Mostly it seems to be a tonic that one might use once a week not everyday water. If you yourself take ACV for health would you add it to every glass of water you drink? I used ACV for the hottest days of summer but then just switched to the vitamin-electrolyte powder one gets for chicks. The feed store in my new location doesn't sell that in the small yeast size packets so bought an 8oz packet that cost $4.29 and will last years. Used for any post stress/injury, hottest days of summer (replenishing cold water several times a day too) and for first few days of hatched/shipped chicks.