As easy as guppies may be they still are easy to kill too.
Do you know your tanks stats IE Ph Temp Ammo Nitrite Nitrate? Was this a new tank? Is it cycled? Did you rinse your stones and fitler b4 putting it in the tank? Were they petsmart or petco fish?
To keep a happy guppy tank you want this.
Ph 6.8-7.8
Temp 70-80
Ammo 0
Nitrite 0
Nitrate 10-40
2 females for every 1 male
The petsmart petco thing is a personal pet haha pev of mine. I have had my tanks I have 3 currently a male a female and a birth tanks all cycled. A week ago I bought 4 fish at petco against my better judgment but they were so cooll looking i had to have them. took them home put them in a container added tank water to thier bag water 1 cup at a time for 3 hrs then added them to the tank after 1 week I have 1 left alive the first 2 died within a day the 3rd 2 nites ago. Not a happy camper and I am kicking myself for not listening to myself. Atleast they have a 15 day return on all fish.
Also if you do get the tank set up and going and you get guppies that stay alive you will quickly find that having males with females you WILL have babies. Understand they can have 10-100 in 1 drop they store enough sperm to drop every month for 5-6 months without mating. Just something to keep in mind. I started with 1 male 1 female I now have 6 males in 1 tank 2 females in another tank with 57 fry 1 month old and 20 more fry 2 weeks old in my birth tank. And the mom that droped the 57 is due any day again.
Good luck and I hope you are able to get alot of joy out of your guppies.