there is alot of thing u need to monitor besides only the ph.The main objective is not to overstress the guppy which will slowly leads to death.Alot of ways can overstress the guppy easily
-Sickness(once a disease is spread among guppies, it will be very troublesome to deal with it.)
-Mating Problem(Female guppies after being pregnant still being chased by male guppies.Once notice Female is pregnant, u need to separate her)
-Temperature.(make sure not direct sunlight or poor ventilated rooms)
-extremely strong current.(Some peeps bought strong air pump which create extreme current in the water, this could stress the guppy as well,best recommended is motionless water with oxygen)

this is what u shud take note.

There is still alot of things u need to take note which i ommited. Because to futher on means u are indulging urself into keeping guppies.