Posibles problemas

it is 40cm

Why the 20/4 light schedule? It could be making the dli too high? Just trying to see what variable it may be. If they are autos the 20/4 should be fine, I grow mine 24/0. If it’s a photoperiod they like 18/6 better. Do you have the photone app or a ppfd meter?

That one is auto, there are 5 other photoperiodic ones, they are at 20/4 because the photoperiodic ones are still seedlings. When they have leaves, all will switch to 18/6. I’m just taking advantage of the first few days to give them a bit more light until the photoperiod-dependent ones grow. Yesterday, examining them, I saw the burns on the leaves.

I would raise the lamp 5 - 10 cm further, see if that helps.

If this is Biobizz’s light-mix it isn’t a coco grow . . . more of an organic substrate with a lower EC than say All-mix, more like Happy Frog vs Light Warrior seed starter.

Their coco product is called Coco-mix.

Yes, I never said I used coco, it’s substrate, yes it has coco, but it’s lightmix substrate.

No, you didn’t but others who posted thought it might be. No offense intended.

Second message from him, it’s in the one above.

I just raised the LEDs 15cm, although I don’t feel enough power to burn the leaves; in fact, it seems like little light to me, though I clarify that this is my subjective view, because it’s the first time I’ve cultivated with LEDs; previously, I always used HPS.

If you notice, it looks “sad” with its leaves drooping, wilted.
The spots are not on the new leaves, only on the false leaves; the apex is still pale.

I also attach another photo of the larger photoperiod plant, where the apex also looks perhaps a bit pale, even though it hasn’t even grown leaves yet.

With led’s it’s not the heat that burns it’s the light itself. Led’s run cool so you don’t feel the heat except what comes off the heat sink and driver. The pale leaves just look like new growth looks. It’s a bit paler than hardened off older sections of leaves. The center has more pale that the outer leaf on the meristem. The tips of the leaves are the first parts to be exposed to the light and harden off faster.

I also have a 240 Watt lamp; according to the manufacturer, it would be for a 1.2 m × 1.2 m tent during the growth phase and for a 1 m × 1 m tent during flowering.
My tent is only 0.6 m × 0.6 m. As long as they are small, I place a plastic cup over the plants so that the humidity for the plants is at 80%, and I keep the lamp at a distance of 45 - 50 cm.
I have already noticed that the small plants stand completely normal in the morning and then in the afternoon start to let their leaves droop a bit; I think they have then received the maximum amount of light they can process in

It’s actually very possible, I took the photo when I posted, and I had just turned on the lights, they were in the dark for 4 hours.

Thanks for still being interested in helping, yes, I thought the same, but I see them too pale although it could be normal as you say, the burns on the leaves, on the other hand, not so much, the LED is relatively far away, now at 60, but they were at 45, and with the power at 25% which would be about 60w, do you think they could have gotten burned because of that distance and such low power? Right now, what worries me is the accumulation of those 3 factors, which are the burns, the size and decay, and the paleness.
In a way, I understand that the growth is due to the hormonal treatment, as the lateral shoots have continued to grow little by little (perhaps 1 millimeter per day?), but they are bigger than yesterday, that’s for sure.
Likewise, I lowered the power to 20% and raised the LED 15 cm, I hope that solves the burning issue, if the paleness is normal, I should think that I started the hormonal treatment too early, or it was a very high dose.

these are the LED manufacturer specifications

With that output for the light I don’t think there is any light burn. There could be light fatigue happening from the DLI being too high but that should show with a droopy plant in the later hours of the day. I have to admit your situation genuinely intrigues me as I’d love to figure out what’s going on. Unfortunately I’m stumped.

something is going so wrong, pic of this morning. (5 min ago)

They’ve had about 12 hours of light now. Yesterday I lowered the water pH to 6.2, as the previous ones were at pH 7. Also, I moved the LED light further away. This time, two almost dead leaves have appeared, curled inwards, with a burnt feeling to the touch. If you touch the damaged leaves with your fingers, the leaf is very thin, without hydration, like dry. I imagine it must be the watering. I lowered the light intensity and moved it away, so I rule out the light as the cause. These are only the first true leaves; the new ones look good.

Hopefully not Tobacco Mosaic Virus (TMV)
Just let them grow and don’t always touch them
If it’s only on the first leaves and the new ones show no changes, I would let them grow.

Best regards, I hope you get it under control

Good eye @herr_gruen

I just wanted to point that out too

But yes, that really looks like an infestation.

Thanks, @KilliczGe, a good magnifying glass should solve the mystery now. After that, we can see how to proceed against it.