Over & under-feeding and how to tell the difference

[TheDude#1]

Hey all,
Well thought i'd add the topic as at the moment i am having some yellowing of my plants and i am unsure as to whether its under or over feeding. i am now in the middle of week 6 of flower on a blueberry skunk that takes 10-12 weeks total and i have started to see some serious yellowing of the fan leaves (mostly the older growth) but i am unsure if it is due to under or over feeding! Also some of the laeves are curling up and i am not sure if this is related.
Can anyone tell me the easiest way to tell the difference between the 2 or what the different symptoms of the 2 are.
Any help or info would be appreciated.

 

[Classyathome]

Fan leaves do die - if it's older growth, could be that...

Pics would be helpful - as would details about the grow.

Also, the search function is excellent...

 

[TheDude#1]

Hey m8,
I think i may know what it is. I think i have have a Mg deficiency. I have the yellowing in between the veins and the canoeing (curling up) of leaf's starting which i have read in some threads and the sick plant guide are all signs of this deficiency!!! So now that i think i know the cause of the problem i can now start to fix it!

 

[I N Hail]

http://icmag.com/ic/showthread.php?t=11688