It is dependent on the grower really. I use Promix, which is basically the same thing as Sunshine. I have grown with a ph of 6.3-6.5, 6.5-6.8 and 5.6-5.8. I grow at 5.6-5.8 now, I noticed around 6.5 and above I begin to see micro deficiencies in the stretch stage and when I stay below 6.3 I don't.