store bought guppies can be tough to keep alive. usually if you can get a store bought guppy past 3 weeks, then you got good ones. hard to tell, but if those red things i see in that tank are shrimp, and you are keeping them alive, its for sure the guppies themselves. sometimes its the fish are weak, sometimes it is the water they were raised in compared to yours. im told many breeders will raise them in mildly brackish water, and the transition to pure fresh water too fast can be hard on them.