Yellow tips: Is this light stress? See pics

On my 40 day old autoflower I have been seeing the leaves curl upwards and the leaf tips turning yellow. The internet told me this may be light stress, can anyone confirm? I have attached pictures.

It would surprise me, because I have only a 100w lamp at 34cm distance and I have dialed it all the way back to 50% now.

The plants look pretty good. To me, it doesn’t really look like light stress. Maybe nute or ph related, looks like you’re in coco. What, how often are you feeding, ec, ph? Whatever the reason, they don’t look bad.

The most common reaction to too much light is that the edges of the leaves curl in. That's referred to as "canoeing" or "tacoing". Your leaves are ruler flat.

A 100 watt light at 34cm at 50% is a bit low but OK. It wouldn't hurt to go by the manufacturers recommended settings.

Answers to standard questions - nutrients, pH, temperature, RH, watering practices, etc.

I don't think that's light, If that's coco...run nutrient through the pot to get your regular run off and test the ec/ppm of that?

Idk about light burn but you can rule out nutrient problems by doing the above, do you have a ec/ppm meter?

I would think light stress would cause the leafs to curl down away from light. The plant looks healthy. Looks like others said nutes or pH. Or in my mind I don't run in coco but heard others discussing it recently and were talking about how you have to keep coco wet consistently so seems the plant is fine and maybe the strain is just a little bit reacting to that?

Now I’ve grown a fair dozen of autoflowers and every time they get yellow tips like this. Some more than others. I think it’s a ruderalis trait. Perhaps they are more sensitive to K (potassium).

They usually yellow right around stretch. Eventually they go black and crispy and fall off (the tips).

Never figured out exactly what it is but the plants seem to grow fine even with the yellow tips

Phytoplankton said:

Maybe nute or ph related, looks like you’re in coco. What, how often are you feeding, ec, ph?

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Delps8 said:

Answers to standard questions - nutrients, pH, temperature, RH, watering practices, etc.

Click to expand...

Star Dog said:

Idk about light burn but you can rule out nutrient problems by doing the above, do you have a ec/ppm meter?

Click to expand...

It is not coco. It is Plagron Allmix prefertilized soil, which admittedly has a PH slightly too high at 7,5. I've been trying to get it down with concentrated lemon juice without succes and will be switching to proper PH-down soon.

Since the soil is prefertilized I have not been feeding nutes during veg, but I recently started giving it Plagron Alga Bloom since it started bloom.
I have been watering every few days and letting it dry out after each watering. These days I am giving it about 1L and the plant lasts about 3-4 days on that before it's dry and needs watering again. I use a moisture meter to measure the moisture, as well as lifting the pot and feeling the underside of it for dampness.

Nutty sKunK said:

Now I’ve grown a fair dozen of autoflowers and every time they get yellow tips like this. Some more than others. I think it’s a ruderalis trait. Perhaps they are more sensitive to K (potassium).

They usually yellow right around stretch. Eventually they go black and crispy and fall off (the tips).

Never figured out exactly what it is but the plants seem to grow fine even with the yellow tips

Click to expand...

Thanks! Maybe it's fine then. Guess I'll turn my lamp back up high!

It is interesting you mention potassium, because earlier in the grow I took off some leaves which appeared to indicate a potassium deficiency. It hasn't shown up since, but I suspected at the time the slightly high PH level was perhaps inhibiting potassium intake.