Leaves starting to show signs of something, HELP w/Pics

These are Sweet Cindy's non-feminized and are 4 weeks into Veg. They are in hydro buckets feeding on Flora series (half-strength) of recommended which makes me think it isn't a nute burn but then it sure looks like it. I heard that nute burns are throughout the plant and deficiency happen in the older or bottom leaves first is that true? The ph of the solution is between 5.0-5.5, room temperature 75F with plenty of air movement. They just starting showing problems yesterday and I'm confused whether to add nutes or flush since if I guess wrong then it will get even worse. Can someone who knows what this looks like give me better details on what it is or might be? Any help is appreciated, thanks.

may be a magnesium deficiency

It is Magnesium or Potassium a little early to tell.. This book saves plants, I buy it though! However there is a preview online that will tell you how to troubleshoot your plants.. here is the link
http://books.google.com/books?printsec=frontcover&id=r9a9QZI9wnwC#v=onepage&q&f=false

May want to raise your ph to closer to 6.0.It might be too low for nutrients to work properly.

warfey said:

May want to raise your ph to closer to 6.0.It might be too low for nutrients to work properly.

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5.0-5.5 is optimum for hydro from what i have read, i don't grow hydro although it seems that's not the problem the because rest of the foilage looks healthy.