You need a quality ppm and ph pen is you want to do this shit right.
And this is a hard one for the "whoa dude, I'm like growing weed and stuff" crowd. KEEP FUCKING RECORDS!!
Ppm, ph, how much water they drank, observations, etc. Take this shit seriously.
Because when you do, all kinds of revealing patterns are found and you learn to feed and manage your plants without reading bottles or instructions.
I haven't read a nutrient bottle in years. I know I know, it sounds arrogant and condescending but that is just my style. Spend a little money, keep records and read. Read read read.
Good luck and let us know how it progresses.