10 mg per drop (standard strength)
I think we need to pin this dosage down here, before somebody does a mad scientist thing here and kills a Corn.
The above recomendation of 20 mg. per fl. oz. is pretty dang strong, even PH corrected,
and the dose of 1 or 2 drops per pint of water ( 1 pint = 473 + ml ) is not even remotely close to 20 mg. per fluid ounce concentration, I have to say
1 drop per pint equals 8 drops per gallon.
When in doubt proceed cautiously.
I use three drops per gallon
(1 U.S. gallon = 3.7854 Liters) .
and my menagerie of critters (birds,dogs,cats,chickens & pot bellied pigs) will all readily drink it.
Although I only use one drop per gallon for "everday use" with my reptile water to control biological growths in there water Dish.
Water is changed everyday but,
my house is pretty warm most of the year and warm room temp. tap water will breed bacteria's in it very quickly, I'm sure.
We have "hard" water here with a naturaly high calcium content which naturally lowers G.S.E.'s acidity to an acceptable level.
I use a PH test kit with a liquid regeant agent called
"Bromothymol Blue" ,
obtained from the aquarium section of your favorite store, and it works well for me. A couple drops in to a small sample will show you the PH level by changing colors ,correct your PH until the desired Blue, neutral PH color is obtained, very simple and easy.
Water hardness tends to fluctuate season to season, at least here in Arizona.
10 drops per gallon is recommended to human beings to purify natural sourced drinking water ,
( back country hikers love this stuff,
they commonly add a little powdered gatorade to mask G.S.E. natural bitterness )
It has been tested and found effective in lab studies against hundreds of pathogens at 10 drop per gallon concentrations.
1 drop = 10 mg , 10 drops = 100 mg per gallon

1 drop per 12.8 oz.water is the same as ten drops per gallon.
At those concentrations it will kill most, if not all of the micro biological critters (amoeba's ,bacteria's , etc.) living in that water.
Hospitals use concentrations of 30 drops per gallon to sanitize carpeting, it kills hard to kill "staph" Germs, etc at those concentrations.
I disinfect caging/enclosures, bowls and even parrotlets water bottles with 30 drops per gal. concentrations.
This is not written in stone, this is not gospel ,and your mileage may very well vary.
Proceed with caution and attention to detail
if you do choose to "treat " your snake with Grapefruit Seed Extract.

Following up a g.s.e. treatment with pro biotics is a good thing too, but that will be another thread.
When in doubt, theres always your friendly local reptile specialist vet to consult about ones sick snake
