Have I been starving my plants?

Hi
Have I been starving my plants? I have been growing in Soil under a 400 HPS during flowering for the past 9 months. I have been having average yields from my plants. I like to keep things quite simple but at the same time ensuring that the light, air, water (PH) and food are kept to within the recommended guidelines. I have been using the grotek nutrients (http://www.grotek.net/). There is a chart which specifies the correct amounts of each of their products to add to the water at a given time during the flowering stage.
I have purchased a PPM meter to-day and tested my water after I added the usual amounts of everything; I was surprised to see that the reading was approx 550. I have asked a few guys who have been grown for years and they recommend that I should at least have a ppm between 800 and 900 for their first/second feed and to work my way up to approx 1400 and 1800 for the final two weeks.
Do you think my friends are correct? Should I always increase the food to bring up the PPM. Have I been starving my plants?

I'd like to tell you the story of my success.

"I simply followed the directions" the end .


I may use Fox Farm but the principal's the same.
If I follow the directions to a "T" then a problem can be fixed by process of elimination.

I know this is a older thread but i was in the same nute boat sort of speaking.im a dirt farmer in 5th week flowering using fox farm line up,watering ph 6.3-6.5,tap water at 220ppm,1000watt hps and also just bought a hanna ph/ppm meter and been mixing up my nutes as advised by FF and used the ppm meter and to find out my ppm ratio was 750ppm with nutes so i bumped up a bit of cha ching and tiger bloom to bring the ppm's up to 1085 so i guess 1100ppm rounded.i am thinking all this time i have been under feeding them.so i am at 5th week flowering at 1100ppm and FF is calling to be between 1540-1680 week 5 flowering,it seems like i would fry the shit out of them at that ratio,and im a chicken shit so i think 1000ppm is a good in between number...any thoughts

any experinced ppm farmers out there...lol