Is this a deficiency (burnt seedling tips)?

Hi growers, I've been doing some research on here and haven't been able to come to a solid conclusion.
Was hoping you all could take a look at my situation and provide some insight into 2 questions before it's too late.

1. Why are the tips of one plant burning?
   • I've seen some people on here say N deficiency, others say CA deficiency, others say Mg. I felt like only 8 days in is too early for nutes but if it's truly N deficiency I'll start feeding them.
2. Why is there seemingly some kind of "frost" on the leaves?
   • I haven't been able to find many answers to this question other than it may be some kind of fungus and that's it's likely too late to fix.

Key info:
- planted 11/26/23
- watered every 2/3 days (whenever soil dries up) w/ph 6.5 water
- Temp 70-80F & Humidity 68-74%
- led light on at 40% for 18hrs per day & oscillating fan running for 7 hrs per day.
- treated medium today with Warhammer fungicide (manufacturers dosage)
- can answer any other questions as necessary

I'm really hoping anyone can provide some suggestions on what's going on and how to fix it.

Plant 1 - growing much slower than the other, tips are burning and minor frost on catyledons.


Plant 2 - growing quicker than plant 1 but minor cotyledon burning and more frost w/ tiny yellow spots on true leaves.


Finally, I've seen several people say that seedlings will generally fix themselves after the first 2-3 sets of true leaves but I'd rather ask and not need to then vice versa.

Any insight would be greatly appreciated!

What soil are they in?

It looks like nutrient solution was dried on the leaves or it is powdery mildew.

If the soil isn't too hot for the seedlings the burnt tips could be mechanical damage from the fans.

Modern Selections said:

What soil are they in?

It looks like nutrient solution was dried on the leaves or it is powdery mildew.

If the soil isn't too hot for the seedlings the burnt tips could be mechanical damage from the fans.

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They are in Tupur soil. Those brown ish pieces you see at the top of the soil were white to start with, looks like they burned brown or something. Should I raise the lights or something? Lower temps?

That's normal sometimes. Imho usually due to moisture/humidity on the fresh sprout. No issues.

Adverb said:

They are in Tupur soil.

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Royal Gold Tupur is coco, not soil. Start feeding it around 0.4EC (200PPM on the 500 scale) at lights on every day to at least 10% runoff, pH'd to 6.0-6.3 for 5-7 days and then increase the nutes to around 1.0EC. In another week after that, lower the pH down to about 5.8-6.0 for the rest of veg.

As for light, saying "LED at 40% for 18 hours" is meaningless without knowing the wattage of the light.

ec121 said:

Royal Gold Tupur is coco, not soil. Start feeding it around 0.4EC (200PPM on the 500 scale) at lights on every day to at least 10% runoff, pH'd to 6.0-6.3 for 5-7 days and then increase the nutes to around 1.0EC. In another week after that, lower the pH down to about 5.8-6.0 for the rest of veg.

As for light, saying "LED at 40% for 18 hours" is meaningless without knowing the wattage of the light.

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Quick follow up to this, I've read that your watering amount should be about 1/4 of the size pot you are in. Would you say this holds true in your experience? I've got them in a 10 cubic inch seedling tray so planning on giving about 4ml of water with nutes mixed. Is this about right?

Adverb said:

Quick follow up to this, I've read that your watering amount should be about 1/4 of the size pot you are in. Would you say this holds true in your experience? I've got them in a 10 cubic inch seedling tray so planning on giving about 4ml of water with nutes mixed. Is this about right?

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Does the tray have drainage holes? If not, poke holes in it with a pen.

The most optimal way to water in coco is to always have nutrients in the water and water until at least 10% runoff comes out the bottom. That means if you put 100ml through the top, at least 10ml should come out the bottom (always remove the runoff so the plant isn't sitting in it). Coco is not soil and takes a different fertigation protocol - forget about most things you've read about growing in soil.

How much it will take for that 10% runoff to occur depends on things like how often you feed per day, plant size, environment, etc., but the key in coco is to feed at least once a day and to get at least 10% runoff each time you feed. If you don't get runoff, then you will eventually get salt build up in the coco and start frying the plant.

Also measuring the runoff EC will help assist you here - this will give you indicators as to what the salinity of the medium is at.

ec121 said:

Does the tray have drainage holes? If not, poke holes in it with a pen.

The most optimal way to water in coco is to always have nutrients in the water and water until at least 10% runoff comes out the bottom. That means if you put 100ml through the top, at least 10ml should come out the bottom (always remove the runoff so the plant isn't sitting in it). Coco is not soil and takes a different fertigation protocol - forget about most things you've read about growing in soil.

How much it will take for that 10% runoff to occur depends on things like how often you feed per day, plant size, environment, etc., but the key in coco is to feed at least once a day and to get at least 10% runoff each time you feed. If you don't get runoff, then you will eventually get salt build up in the coco and start frying the plant.

Also measuring the runoff EC will help assist you here - this will give you indicators as to what the salinity of the medium is at.

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I can't thank you enough ec. The trays do have holes, I got plant saucers to catch the run off today. I think they'll definitely need more than what I was calculating for 10% runoff, I'll give them a bit more and see what my runoff looks like. I appreciate your help my friend.