Rehabilitate them in the fridge. Prepare some sugar water put a lid on your jar and place them in the fridge to slow down and recover. They can stay in the fridge for 3 days up to a week. It may take a brew or two (2 Fermentation cycles of 48 hours) for the Kefir Grains to make great kefir and reproduce at a steady rate.
Wake up your slow grains by creating the optimal environment for them. You don’t want to starve your Kefir babies because that will cause their metabolisms to slow down resulting in slow grain growth. Make sure that you feed your Kefir Grains every 48 hours with a fresh batch of sugar solution. Nutrients also play an important role here, they love unrefined sugars and molasses mixed together. They love apricots and ginger slices. Keep them surprised with the sugar source as they thrive on a variety of nutrients introduced on a on-and-off-basis. For example one week for apricots, the other week for dates, one week for ginger slices, then a week for raisins and a couple of days off, starting with apricots the next week.