Tomatoes with twisted purple leaves

[KreegDaddy]

Hello everyone! I am new here but popped in to see if I can get some help with my tomatoes. I have embarked on a new growing adventure, trying my hand at hydroponic gardening. My tomatoes started out pretty good but the leaves did always have a purple underside. I've noticed this before with young plants in soil culture but it had never caused me any problems until now. Some of the leaves are actually turning up and showing the purple underside and one plant in particular has the leaves kind of twisting. I don't see any signs of nutrient burn. But from what I've read the purple is indicative of low phosphorus. The nutrients that I'm using are GH grow, micro and bloom. I'm following the insructions given from GH themselves. Right now I am in about week 4. I didnt keep a good record of exactly when I started, oh ya , and I started them from seed. My other plants seem to be doing pretty well.

My PH is at 6.0 and the room temp does vary quite a bit as my system is in a green house in SW Colorado, it can get 92 deg mid day and about 55 during the night.

If any one has any ideas to help me correct this problem, I would sure appreciate hearing them. Thanks in advance!

PS, i'm not sure why but I cant seem to post more than one pic.