You can make your own liquid fry food. Take a couple of flakes of food, put in a small glass jar and set in direct sunlight. After a few days, the glass will go cloudy. This is a batch of infusoria. I add a couple of tablespoons of the liquid each day, usually in the morning. I have a tank I set up for a friend and her guppies had babies, and they've been doing quite well on that. Also, when you feed in general, I would also crush the flakes even more than usual.
Val