Additive to boost P levels in vegetating plants

Currently I'm using Fox Farm Grow Big as the food for my vegging plants. I have noticed some reddish stems that seems to be indicative of a P deficiency. I was wondering if anyone knows of a good way to boost the P level of the water in the reservoir, either via an additive or mixing another hydro nute w/ the Grow Big.

Grow Big's NPK is 3-2-6

One possible solution that seems viable is to pick up some Dyna-Gro, which has a NPK of 7-9-5, and mix it in smaller portions w/ the Grow Big.

Thanks

I'd like to know this as well

earth juice bloom works for me. i think its 0-3-1