Red Branches?

[elklake]

I have a pach of plants in my growroom that were all started from seed, on the same day with the same soil and conditions. First of all I am on day 36 and my plants are about 19 inches tall with five sets of main leavs and about 1 inch sprouts at each leaf base, is this about where I should be for that amount of time? And my other question is that on one of the plants the leaf vain and the stem to the main stalk are bright red, plant looks great growing same as the others, anyone know what this could mean? this is my first grow.

[peanutbutter]

needs a little cal/mag

 

check the Ph by checking the drainage water.