hydrolized

Just wondering what people are seeing from week 1 of flowering for their hydro ppm's..

A buddy has some Big Bud and for the first week of veg they wouldn't take any more than 300ppm, second week of veg wouldnt take anymore than 450ppm, now they are on day 10 of flowering and were at 650 dwindling down 10ppm per day so she brought it up to 700 and got burnt tips, she had to bring it down to 650 where it stays..going by the sacred saying if your ppms are going up the plants are drinking more water than food ie your solution is too stong...so it staying at 650 says thats what the plants will take. I keep reading/hearing about all these people using the 8-16 Lucas method from Week 1 having ppm's in the 1100-1600 range without problems....why can't she even go above 700 without burning? Is this normal?