Nutrient burn? heat stress? lack of nutrients? plz help!

OKay, so I have 6 plants from clones that im closet growing. i transplanted them to 3 gal buckets September 7th. They have been looking okay but I am noticing what seems to be burns on the leaves. I have grown before but I got lucky.

They are under 2 150watt hps for 20 hrs and get plenty of ventilation. The temps range 75-78 throughout the day. I have fed them with nutrients 2 times since first planting them. I used fox farms nutes and used a very little amount. I make sure to PH test everything first.

Each picture is a different plant. Please let me know what you think

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could be nutrient burn. those clones don't look enormous yet, so their roots may be a a bit vulnerable.

usually after transplanting i will only water for a month, as the soil should contain enough to feed the plants by itself.

perhaps someone else could chime in though, as my answer is far from 100% certain.

do you think i should flush them?