Hi, sorry but it really isn't a good idea to use Vitamin C drops in their water. Here are some reasons why. 1: Once the Vitamin C is added to water that is exposed to air, half its strength is lost within just one day. 2: It might change the flavour of the water so the piggies don't want to drink it as much. 3: You can't really know how much Vitamin C they are getting from it. 4: The drops tend to promote algae growth in the bottle.
The best thing to do is include one Vitamin C-rich veg (or fruit, but fruit should only be fed 1-2 times a week due to high sugar content as well as acidity. Too much acidic fruit, such as apples and oranges, can cause mouth sores) in your piggie's daily veg mix such as kale, brocolli, and sweet bell peppers. Any colour of pepper is fine, but red contains the most Vitamin C. An 1/8th of a pepper per day will suffice.
And, of course, dry food pellets give them additional Vitamin C too. As you live in the USA, Oxbow Cavy Cuisine is a good choice.
Alternatively you can supplement their diet with Vitamin C tablets or in liquid form (which you feed from a syringe). Don't feed multivitamins. Remember not to overdo the Vitamin C though, extremely high amounts lead to problems. The average piggy needs between 10 and 30 mg of Vitamin C per kg of the piggy's weight (piggies usually weigh around 700-1400g, but it does depend on the piggy). Pregnant/nursing/malnourished piggies will require more Vitamin C than normal. You might find this page useful:
http://www.guinealynx.info/scurvy.html
It may be a good idea to read these too:
https://www.theguineapigforum.co.uk...or-a-balanced-general-guinea-pig-diet.116460/
https://www.theguineapigforum.co.uk...veg-and-fruit-list-with-vitamin-c-grading.42/
If you have any more questions, feel free to ask.
