new growth bright yellow

hi everyone, its been a while since ive been here (no internet :()
i couldnt find the form to fill out so i will do my best to provide as much information as i can.

i am growing indoors in a 100cm x 100cm budbox
i am using Gold Label's Special Mix as my medium
PH is about 6.5 - 6.7 and run off is almost the same
i am using IONIC's hydro bloom and boost
i am using 2x 600watt HPS in cooled tubes shades 18 inch from tips
temp in tent when lights on = 78 - 80 degrees and 70 approx when lights are off.
humidity is approx 40%
plants are 8 days into flowering cycle and are aprox 16 inches high

i know the first thing your going to say is im using the wrong nutriants but i used the same nutriants last time with no issues and i am trying to finnish what i have left.
i dont know why but all the new growth seems bright yellow (not light green but yellow), the new growth is coming through very fast. its mainly the plants directly under the lights which seem to be yellowing and all the others seem perfect but the odd thing is there is little or no heat on the tips. i have a 65w fan constantly blowing between the lights and the tops of the plants to remove any heat and the plants only appear to move as though in a slight breeze.
when i grew the same strain the other year i was able to get the lights much closer without any yellowing so i am wondering what could be wrong? other than the yellowing they seem fine. i am sorry i dont have any way to take any pics yet though i know they would help greatly.
thanks for your time

Yup. Pictures would help.

Gold Label peat or coco?

When was your last flush? from Ionic's website: "IONIC is manufactured from the purest and most soluble mineral salts, not from harsh industrial chemicals, and is very gentle for the plant."
Salts build-up over time and affect uptake.

How old are your bulbs?

What source of micronutrients are you giving 'em?

hi, its the gold label peat with vermiculite.
i transplanted them 8 days ago from 10cm square pots into 6ltr round pots, they were 12 inches high when poted and put them strait into 12/12 flower cycle from veg stage, not sure if i should have veged them a little first in those new pots.

im pretty sure there wouldnt be any salt built up quite yet as ive fed them half the suggested amount (3.5ml per 1ltr of bloom and 1/2mil per ltr of boost instead of 1mil per litre) i feed on odds days and just water on even days so one day they get water then next they get food n so forth.

i dont use anything else no other chems etc.

i had a 2nd close inspection and i could see deep in the veins they are green but you have to look pretty deep to see it as there really is just too much yellow. the bulbs are pretty old now so that is something i didnt stop to think about, i may invest in some new bulbs while i have a few pennys left to spare.
thanks for your reply, just wish i could get a few images uploaded as it would help.

Do you water till runoff, or give a set ammount per watering?
Same with feeding...runoff or not...?
Are you letting the pots dry between watering/feding? Cannabis prefers a wet-dry cycle. If the roots are constantly wet, it will smother the plant and lockout will begin. If the soil doesn't need water, don't water.

Yellow leaves with darker green veins is a sign of magnesium deficiency.
To treat the magnesium def.: Thoroughly mix 1 tsp (teaspoon) epsom salt (or magnesium sulphate) per gallon of water, raise the lights a bit, and spray the leaves, don't spray the light(s). When dry, spray with clean water to remove any salts left on the leaves. Once leaves are dry, lower the lights back to 'normal'. Repeat in a few days, but only if necessary.

Could also be the plant getting used to the new soil and schedule. If it's transplant shock and PMS (Pre Motherhood Stretch) it'll usually be ok within a couple of weeks of initial symptoms and they should start filling out and uptaking nutrients.

These are the most likely causes, but not having pictures makes it harder to pin down.

for the moment i have turned off one light and left only 1x 600watt hps on and raised it another 6 inches as i have no magnesium supliments yet but it is only the plants directly under the lights that are effected, all the outer plants seem perfect. they have stretched a little, about 3 - 4 inches but they are exteamly packed with nodes showing very little of the internodes so i guess they still have a lot of stretching left to do.

will purchase some new bulbs though tomorrow and see if it helps, its long overdue. will get some salts too and give that a try.
i do normally water about one third of the pot capacity and when feeding but by the next day the pots are dry and light in weight so i asume they need watering again.

thanks again the help is appreciated

im having a similar problem with my bubblegum strain. i have attached a picture as to increase the odds of possibly identifying what the problem may be.....:(

they are growing in cocoand are receiving a aact once a week, nutes between along with plain filtered water.

just tested the ph runoff of a fresh water rinse: 7.06
ppm: 648
i feed heavy 16 bloom a and b and prime, humbolt's deuce deuce, ginormous, and honey.
the tea feed gets brewed with ancient earth by GH, molasses and sea kelp


any ideas brother?:jointsmile: