walmart...5$ ph test kit in the fish section....it comes with a little test tube, you fill it to the line and add 3 drops of solution that comes with it and the water changes color...match the color to the chart that comes with it and your done. one of my best purchaces for my grow. i had probe one and it was garbage. lemon juice for ph down is like $0.79

Walmart.com: Freshwater Master Test Kit: Fish

this is the fancy one, they do not sell the one i am talking about online i guess but you can get the idea from this.