you need two things champ. The first is a ph pen, they run about 20 bucks and I would recommend the hanna ones ebay hanna ph pen with the long black rod on the end. That is the probe and it is hot swappable which means when the sensor fails you can replace it without replacing the entire unit. Keep ph below 6, somewhere at about 5.8 is what most recommend. Personally I find ph to be less of an issue the longer the plant is alive. I regularly give un-phed tap water to my flowering plants when it's time to flush or rinse off debris.

The second thing you need is a ppm meter. They run about 20 bucks as well. Dont buy an expensive one, just buy the cheapest ebay ppm meter

You could probably get these in a set if you looked around. Cheap is best since they tend to fail or get dropped on the ground or in your water.

I keep ppm's @ 700 for vegging plants and work my way up slowly over the next few weeks to 1400 ppm for full flowering and full on vegging. For my mothers and clones I use a ppm of about 500 as I dont always want them to grow really fast right away. A low ppm keeps them growing slowly and the second I increase ppm's they begin vigorous growth.

Pens rock and once you learn how to incorporate them into your system, they make for quick easy checks with the comfort of knowing exactly what's going on or not going wrong with your grow.