Need sum help, leaves r turning yellow and browning off????

Using all advanced line in the start of my fifth wk, connoiseur a/b as a base...temp is about 87f humidity bout 60 percent, sunshine pro-mix 4 in 5 gallon pots and buckets first time using the sunshine mix, 600 watt hps and using 3 led panels...checked the soil and is at 6.5 ph i giv-em nutes at 6.4 ph and try to stay under 1400ppm...well the older leaves are yellowing then turning brown and crispy...new growth looks fine, but some when all the older leaves are gone looks like it is affecting the new growth, the buds are smaller than the healthy plants, just gave them some revive by an three days ago, going to try to use as a spray tonight,,,any advice????

I am not an expert grower and you seem to be doing fairly well in terms of setup and quantity. There are only two pieces of advice I am able to give, The back light in the 5th pic looks like it's too close to the plant. I would raise it up a half a foot or so. For the main question involving the leaves turning yellow and falling off. It's probably a deficiency of some kind. Judging by the first pic I'd say it's a common nitrogen deficiency because the loss of green is starting at the edges and making it's way inward. Also it is starting on the older leafs which would indicate a nitrogen deficiency and would eventually effect the rest of the leaves. It is very difficult to tell by the pictures as well as each plant may have it's own individual problems. I'm sure someone with more insight into growing will be able to help you shortly. Stay strong until then.

Sincerely,
Captain Jack

I agree with the captain but it could also be a magnesium deficiency