Making your own hummingbird food is easy to do and costs a lot less than store bought mixtures.  Be sure when making the food that you don't make too much because after it sits for a while it will grow mold, even if refrigerated.  Also, every time you add more sugar water to your feeder be sure to clean it out with a little bit of bleach.  This will ensure that it is free of any mold that may be forming in the feeder.  It is equally important that you be sure to rinse out all the bleach.  Keep rinsing the feeder until you can no longer smell the bleach.