I used to keep some guppies years ago and I never checked the water parameters.They spawned like crazy and grew up to adulthood fast.So I take it I did something right....lol I used normal pretoria tap water treated with water conditioner and bob's your uncle.The water wasn't even cycled. But this is what I found on google and this is a direct quote "I would suggest a pH of 7.0 - 7.8, harder water rather than softer, and slightly to moderately alkaline" This is what most people recommend.