After my tank had been set up for a while, one of my fish died so I took a water sample to Petco to check and my ammonia was high. Michelle the girl that work there told me to do water changes but to do those by siphoning the gravel also. The poo gets down in the gravel and causes the ammonia to spike. They sell those at most pet/fish stores for around $7-8. After using that for about a week or so your ammonia #should start to drop.
Good Luck
I also have guppies and they are normally peaceful fish, the males will be smitten with most of the females in your tank no matter what kind they are. Just make sure you have a high ratio of females to males.
If you are adding the fish to the 10 gal you mentioned in one of your frist posts you already have enough fish any more and you would have to many. Also, make sure you have some place to put the fry, they will outgrow the 1 gal tank fast.