Diatomaceous Earth?

I visited my local farm and ranch feed store today to pick up a 50 lb. bag of organic 6-2-4, slow release fertilizer. I simply want to mess around with the fertilizer and see what it will do. While at the store, I noticed he also had fifty lb. bags of Diatomaceous Earth. I know from past posts that DE is good to control snails and slugs in the flower beds and garden. I learned it is also a good control of ants, fleas, and other insects with exoskeletons. I am curious if gardeners ever use it as a mineral (calcium) additive in their gardens. The DE is pretty inexpensive when purchased from a feed mill. They also have kelp meal in 50 lb. bags which I will need to investigate. I've read of many gardeners using kelp in their gardens and compost piles. I would appreciate comments on the kelp also.

Ted