Big Bud #2 Lower fan leaves turning yellow then purple. Anybody seen this before?

Kyle Keen Green said:

I did get yellowing of the bottom leaves though when they was ready for bigger pots?

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ShowMeTheWay said:

The lowest fan leaves on my 35 day old big bud #2 started to yellow and then started to turn purple.
I've researched loads and havn't come across anything that describes this hence why i've made this thread.

I germinated the seeds on 1st april using wet tissure in the airing cuboard, then put them into a small six pot propagator tray.
when they had thier 2nd set of proper leaves i then potted on to 4inch pots with a half and half mix of john innes #1 and bio bizz all mix with vermaculite.
The roots filled out the 4inch pots pretty quick so i potted on again into 6inch pots, but this time only had the bio bizz all mix to use.

i'm in the veg stage at 18/6
the set up is a 400w hps, 4inch carbon filter and extractor fan, an RVK one i think. and a small 6inch fan inside the tent.
temps were about 30degrees during lights on but ive got it down to 25 degrees now.
and night time temps are about 17-20 degrees. a few times its fallen to about 15 degrees but not often.
I know cold temps at about 15 degrees can cause purple leaves.....i just don't think that is the case here as the leaves are yellowing first.
the plants are also quite light green.
When the yellowing of the lower fan leaves started i was aware that the all mix is very hot, so i flushed them straight away to try and get rid of some of the nutes in the soil.

i gave the plants 2ml of bio bizz grow two days ago because to me they look deficient in N, but i was wary of doing it as i've only done a few grows and ive never grown any of the strains im doing this time so i dont know how hungry they are etc, so i'm treading lightly.

ive attached some pics of the purple fan leaves i just cut off.
any ideas or advice would be appreciated. thanks!

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