yellow between plant veins - quick fix???

Hey everyone, My plants seem to be doing well for the most part, i think. This is my first grow and i started them before I had internet and therefore no knowledge really. The new leaves on the plants seem to be dark green and healthy however older leaves seem to become lighter and lighter between the veins on the leaves.
- Lights: 18/6 cycle
- Water: Believe to be a little over watered
- Soil: commercial mix (14-14-14)
Any suggestions would be great. Ive read about a lack of potassium or magnesium, but any experience shared would be awesome.
Thanks santas helpers/!!!!

It looks to me like you have a zinc deficiency

zinc deficiency eh??? i just read that a symtpom of zinc deficiency is leaves having wrinkles and my leaves dont seem to be wrinkly. I will search more into this. Is this something to worry about anyways - or am i just being a worried parent?

Looks like pH is off IMO. have you tested your runoff pH?

And yes you need to do something about it.

Magnesium deficency (Fix with epson salt)
Ph to low, i've got the same problems. Check out my journal and you'll see.

i think its probally to do with the water ph though, are you testing it?

okay so i tested the tap water im using with a pH tester that i have for my marine aquarium - sometimes shit comes in handy - and the tap water is reading between a pH of 7.6.

So your pH is too high, this is causing
a lock out of your nitrogen, which
explains the yellow leaves, it is not
magnesium. You would be having
some spotting due to magnesium

Yeah those plants look like they aren't getting N.... If it was Magnesium they would also be "praying" or almost standing upright pointed at the lights.

how old are these babys? they look like they are stretching up for light and the stems look thin. no young plant should need supporting at that age

The plants are just over a month old. However, they werent placed underneath my light until two weeks ago; and at this point the plants were already stretching for light. I understant that they should be shorter but plants were originally grown with a desk lamp. Further. If pH is way too high, how do i reduce the pH so that it is around 6.5?
Also, plants dont need any support. I just removed the sticks to see how they would stand and they are firm. There is also a fan within my growing system for strengthening.
Thanks alot guys

Its too evenly spread to be a direct deficiency, it must be
from pH.... To correct pH, you would need to wait til the
soil is dry, and flush with about 3-4x the amount of water
the pot can hold, you want ALOT of runoff... the water should
be pH balanced to roughy 6.5-.6.7