You need to get a pen to measure the Ph. If you are going to grow at all you need the correct equipment. You can get by with something else but you get what you pay for. If you are going to grow Hydro you will need to measure the TDS-PPM as well as the Ph so make the investment. It's like the difference between growing with 40w fluorescents and 400w HPS. They are just not in the same league.

You should use only RO water, most tap water has chlorine and other chemicals you donā??t want plus itā??s probably hard water and that is not good for most plants.