Guinea pigs need to have vitamin C supplements. I am posting this as a review and proof that guinea pigs do well on liquid supplements that go into water. I have heard others say it makes the water taste bad. This particular one does not. My guinea pig LuLu is always at the bottle drinking and playing.
You cannot feed guinea pigs rabbit pellets alone because they don't have any vitamin C added.
Also, I feel mine little pieces of kale throughout the day. It is loose in a open plastic tub and it helps with the vitamin C as well.