curling problems

Ive been told over fert and under fert, ive been told light burn, can someone help me! And is this normal size at 4 to 5 weeks?

The plants look nice and green to me, except for that leaf. Doesn't even look like the leaf came off those plants.

ProHuman said:

The plants look nice and green to me, except for that leaf. Doesn't even look like the leaf came off those plants.

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What would cause the tips to curl up and yellow?

Could be a nute lockup from salt build up, high EC levels.
Watch the edges of the leaves that are curling up, if they start browning/yellowing, you'll need to flush and lay off nutes for a week or so.
Would help if you mentioned what medium/ec levels etc your at.

looks like a potassium def. to me.

city38 said:

What would cause the tips to curl up and yellow?

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you have not provided enough information for a definite answer. you will probably get responses of various guesses.