The bottom line is to get best effects and know what is going on inhydro you must have a ph meter and a ppm meter otherwise your guessing and will not know what your potential is or your problems should they arise. Can you go without maybe its physically possible but its a waste when a few bucks will benefit you a million times over.
Vegas not sure what kind of device you got. Most are simple pem type meters with a digital display. You calibrate using both 7.0 and 4.0 solutions. You dip the tip in 7.0 solution and see what the lcd reads and then use the adjust screw to make sure its at 7. Then rinse with tap water and dry off and then repeat with 4.0 solution. Then your good to go. Check every week or so and see if it drifts it shouldnt but check. Some meters say store the tip in a storing solution to preserve the accuracy. Then in hydro keep ph at 5.8 or in aero 5.5 and follow your nutes ppm levels per week and your good