leaves growing 'spindly', curling up at tips... what deficiency?

So i have a number of plants in week 2-3 of flower.some are in rockwool in a 3x6 (these are older/bigger) and doing fine. Most however are in a 4x8 in hydroton, and theyre showing a number of signs thats somethings up.

1) theyre kinda spindly and sparse, if that makes sense. Lots of upward growth, not much bushiness.
2) leaves with some slight browning on edges, and most of the tips are yellow/brown and curled up slightly (just the tip though).

Theyve been getting 3 waterings a night (its all hyrdoton so need it, they wilt with less) of roughly 500ppm, pH 5.7. I originally though the nute mix was too strong (had been at 700 or so) so i diluted it, but the problems there.

Theyre under HPS w/ a carbon dioxide system in addition to some standard ventilation fans)

Any ideas? Pictures coming in a few

An upward curl with browing-yellowing on the tips or edges is almost always indicative of heat stress. What`s your room temps like, oscillating fans at all? If the change in dosage hasn`t made a change in a few days, you have just have to cut the tips off your largest fan leaves and start with light mistings in your OFF times. I`ll stay posted, feel free to P.M. if needed. Happy growing

KC

Upward curl, especially in the plant growth stage you're in = magnesium deficit. However, if the tip is simply curled up because it is dead the dead tip is a sign of nitrogen overdose. Either way mix 1 teaspoon epsom salts in a gallon of water or add your cal/mag product and water.

KushCanuck said:

An upward curl with browing-yellowing on the tips or edges is almost always indicative of heat stress. What`s your room temps like, oscillating fans at all? If the change in dosage hasn`t made a change in a few days, you have just have to cut the tips off your largest fan leaves and start with light mistings in your OFF times. I`ll stay posted, feel free to P.M. if needed. Happy growing

KC

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Really don't think its heat stress. Peak heat temps are mid 80s, lows are 60s. Good night-day variation as far as I know. And 2 oscillating fans.

Plus the Co2 should mean its okay even in high stress, right?

Pics in.

Bottom pic - blanched tips still are proof of early nute OD.

hotrodharley said:

Bottom pic - blanched tips still are proof of early nute OD.

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will that reverse itself with time?

hotrodharley said:

Bottom pic - blanched tips still are proof of early nute OD.

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I second this after pics arrived and given your temperature situation. Give a 1-2 day break from nutrient schedule and resume with 80% feedings. A flush could do a little quicker job, but you don`t want to completely rid the medium as this is still premature OD. Remember the plant is vigorous so a slight adjustment on your behalf should help it re-adjust

KC