Help diagnosing mysterious seedling damage

Is anyone able to help identify the type of damage on my seedlings? I have some theories below but would like an eye from an experienced grower

Here is the damage today on one of them, at 26 days old:

Here is the damage when I first noticed it on the same plant, at around 21 days old:

Here is some data about my setup:

I am a first time grower, growing in a DWC hydro setup, following the “Lucas formula”.

Plant Age: My seedlings are 26 days old from the day I put them in a wet paper towel to pop them.

Before the damage was clear to me my reservoirs are 5 gallon buckets and were fed with:

  • 3ml/Gal General Hydroponics Micro (Mixed first)
  • 6ml/Gal General Hydroponics Bloom (Mixed second)
  • A little less than a 1/2 tsp Great White Mycorrhizae (Mixed third)
  • General Hydroponics pH Down to adjust to pH target (Mixed fourth)

Before the damage was clear to me here was my environment:

  • Light: 200W LED 40%-70% power at least 24” from the top of the plant
  • Air temp: 68F-75F
  • Humidity: 40%-60% (was usually closer to 40)
  • VPD: Around 1.00-1.2
  • Water pH: 5.5 - 6.5
  • Water Temp: 68F-71F
  • Water EC: 600-900
  • Water source: tap water
    • Chloramine / Chlorine levels negligible according to water quality report
    • Under 200 PPM out of the tap
  • Water level: .24” below basket, with top feeding ring to help provide root moisture
  • Air stones: yes

Theories:

Transplant Shock - the plant that has more damage now was the more robust sprout in my humidity dome out of my two babies. I waited a day or two for the second sprout’s root system to ‘catch up’ before transplanting, at the expense of the first plants root’s poking out of the rockwool being exposed to more light and air. Additionally, the water level in my reservoirs after transplant was beneath the basket. While I did have a top-feeding ring to help keep the root area wet, the plants were not able to immediately find water below. A couple weeks in I did raise the water level up in my reservoirs and roots have grown into the water.

Splash Damage - I initially had a top feeding ring I was using after transplant to help the roots grow in the basket. It was causing a lot of splashing on the leaves as you can see in the earlier picture.

Great White Mycorrhizae Issues - A youtube grower that had what looks like a very similar damage profile claims it was from bunk great white: https://youtu.be/oK10Cm4L6KI?list=PLdjpcVa8bsh2cLKxPl2ULjMxPc0I1qKF0&t=691

Transpiration Issues - I realized that my humidity at around 45% could’ve been quite low for the seedling stage.

Actions Taken:

I have rinsed the roots in tap water, rinsed the reservoir, and re-fed without Great White

I have purchased a humidifier and keep humidity around 75%, VPD around .4-.8

Overall throughout this I see continued root growth and new leaf growth. I try not to compare to other grows too much but they do seem to be stunted from all this, which is what spawned my initial concern. I hope the babies will turn out OK!

I see water on the leaves in the 2nd pic. It is likely that water exposure has caused issues with the bottom leaves, which already struggle to remain healthy as a plant ages.

I wouldn’t worry about it so long as you have healthy new growth coming in. If you are misting your leaves I would stop. It creates more risks than it could ever provide in benefit.

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Undoubtedly the problem. Those lower leaves resting on Hydroton are also a problem.

Need to lower the liquid to 1 1/2 to 2" below net pot to avoid stem rot and damping off.

You should also be running cal mag and silica. Neither is present with the GH ‘trio’.

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Thank you! My tap water is at least “not soft” – would the calcium & magnesium potentially present there be enough to preclude the use of cal mag? I couldn’t conclude from my reading that tap water means no cal mag necessary.

Also, recommendations on when I should lower my water level? Is it just when there are roots > 2" below the basket?

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As soon as roots grow below the net pot you can discontinue top feed. Over time you’ll want to lower the liquid to 3 or 4" below. This will be a problem in DWC without a check-rez.

Without a solid water report to base off of I would be adding the cal mag anyway: won’t hurt anything. Silica is necessary for plant strength, disease resistance and trichome production.

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I was scrolling to type this.

Also wanted to point out a few other things. This is long beyond a seedling, been vegging for a couple weeks. 5.5-6.5 is too big of a swing to have all the time. Set it at about 5.7-5.8 and reset if it gets above 6.0. You’ll see best growth with air temps around 80f when using led lights. They don’t heat leaves quite as much as hps bulbs so running a little warmer air temp helps to get leaf surface temp to more ideal point. I suspect running air temp warmer will probably raise solution temp, so keep an eye on it and be ready to mitigate res temps.

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