Flying Bandit and other, medical 1st time grow op (Girls need help!)

Hey guys,
So I've recently acquired a medical license to grow. I have little experience as does the designated grower. We have a setup that's been constantly adjusted as we dial in the tents.
The plants were fine for the first couple weeks but started to show nutrient burn. We stopped feeding nutrients as the soil seemed to be loaded with them already. Flushed for several weeks and think we have the soil manageable.
The runoff of water tests at ph 6.9 (goes in no higher than 6.8 and we use a meter to test and balance our pH.
The ppm of the soil without anything added has runoff around 1200 ppm. After we leached the soil it brought it down to around 4oo ppm. Still 3 weeks later and the leaves show signs of what we've been treating as nutrient burn.
The tips turn white and the bottom leaves turn yellow and die. Tips are curled and some earlier leaves had dark veins and very pale green leaves.
I'm starting to think the soil had tons of the wrong nutrients and now giving it anything fails.
The next we think to try is lowering the pH a little more around 6 and hope the overall soil environment lowers to reduce possible nutrient lockout.

Should we flush still?
Should we give anything for a deficiency. Or shall we concentrate on pH still?
These were already set back schedule about a month as i dont want to send into flower until we have some healthy looking plants.
TO top things off we just got the LED light installed and setting it up burned a couple of the plants.
We were running a 400W metal hallide in a 4X8 tent. We have two blower fans with a carbon filter exhaust. Temps are within 22-25 degrees Celsius. humidity 50-75%.
We feed about once a week until water flows from the bottom of the grow bags.
I'll post a ton of pics from the early grow to the current stage so you can see the progression.

Would really appreciate any help. These are 10 plants, 5 each of flying bandit and sorry i forget the other strain. I may be able to ask the donor for the strain info again.
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March
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I will have to make separate posts for April and May as I am limited to 20 images per post.
 
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