Hey man, make sure your PH is at the correct level for nutrient uptake... If its not between 5.7 and 6.5 its gonna block out all the ferts your giving it. The closer to 5.7 you are the more N it will use and the closer you get to 6.5 the more P it will use.
Aside from that, even if your top 3 inches are dry, depending on pot size the center might still be soaking wet, and that would mean your over watering... try and wait to see at what point the plants wilt a little bit, and lift up the pot to feel how heavy it is... then water the correct amount, and check again how heavy the pot it. Now you can make a balance between how your pot should be watered...
i hope you make it through man!
Till then,
keep it green in love and under JAH LIGHT!!

__________________
Everywhere the fire is burning... Destroying and melting their gold... Destroying and waisting their soul...... GROW NATTY GROW sprout it bongo sprout +=

How do I know if my plant needs nitrogen? And if it does, what do I add to increase the nitrogen?

My stems too are a little redish in color...the leaves though are fine and seems to be growing ok at this point.

basically, U can tell what is wrong with your plants by looking at it.. you just have to learn what signs mean what... yellowing leaves usually would be a Nitrogen deficiency... and the purple reddish stems would probably be a Phosphor deficiency but some strains have that in their genetic... Often people mistake ph lock out with nute burn and over watering etc... you need to read up and look at pics of all the different deficiencies and plant problems there are so you can do something about it when it occurs....
good luck man!!
peace

__________________
Everywhere the fire is burning... Destroying and melting their gold... Destroying and waisting their soul...... GROW NATTY GROW sprout it bongo sprout +=

basically, U can tell what is wrong with your plants by looking at it.. you just have to learn what signs mean what... yellowing leaves usually would be a Nitrogen deficiency... and the purple reddish stems would probably be a Phosphor deficiency but some strains have that in their genetic... Often people mistake ph lock out with nute burn and over watering etc... you need to read up and look at pics of all the different deficiencies and plant problems there are so you can do something about it when it occurs....
good luck man!!
peace

__________________
Everywhere the fire is burning... Destroying and melting their gold... Destroying and waisting their soul...... GROW NATTY GROW sprout it bongo sprout +=

The guys post above mine was doubled. He was either really stoned up has a messed up computer...lol roflmfao@him...

red stems are normal on some strains, either that or its too cold, which doesnt appear to be the case. it looks fine dude, can u give us a pic of the black dots? might be spidermites(pray its not!!!)