HELP! Yellow spots on my seedling

[DirtyChai]

Meet Cookie. She's a ~2 week old cookie breath seedling. I have her in a 2x3x5 budget-built grow tent with relatively good air flow/exhaust and sitting under a 1000w full spectrum LED grow light. With the light off, temperatures float around 60-77 with humidity anywhere from 20-50%; however, with the light on, heat increases to 70-95 with similar humidity (we're having trouble controlling our temps). She lives in a 3 gallon planter of organic soil and has not been fed anything but pHed (to ~6.5) distilled water when the dirt is about 75-90% dry to the first couple knuckles. The plants are under a 18/6 light cycle. The tent is currently home to two plants, both of which initially seemed to be growing fine. Let me make it obvious that I am brand new to growing and am not super knowledgeable nor have any experience with this. At first she was growing very fast, quickly surpassing the other plant and up until about a week ago, everything seemed to be perfect. At about the one week mark she started to develop spots on the tips/edges of her first pair of true leaves. The spots start out small and relatively spread out and look almost like a transparent film on the leaf before turning yellow, growing and eventually spreading to the center of the leaf. She continues to grow really fast and new growth seems fine for a few days. But when they open up and mature a bit they get the same spots. Some of the fringes on her true leaves curl as well, so our initial thought was light burn. We immediately backed the light off to 42" from the plants. However, the problem persists. Our next thought is that it could possibly be heat burn or something similar? Keep in mind that all along, the other seedling (alien OG), has been growing completely fine this entire time. If anyone has any input or solutions, please let me know!!!!!!

[GreenAlchemist]

Just to narrow things down a bit, What medium did you plant her in? Did you add any dry amendments to the soil or a premix?

The extra heat could definitely play a roll in what’s going on, having a fan blowing directly on the light, and a small portable AC unit inside can help reduce that to a much more desirable temp.

[DirtyChai]

She's planted in Nature's Care Organic and Natural potting mix. I've read that most organic soils contain the necessary nutrients for seedlings, and the bag says it contains calcium and magnesium as well as other micro-nutrients, so I was planning on waiting until at least week 3 to incorporate dry amendments or chemical nutrients. Thanks for the response...we have a couple fans but a small AC is definitely something to consider.

[MeEasy]

I'm wondering if it's the distilled water's lack of minerals that has caused lockout

[Acology]

pots too big unless its a auto

humidity in the 20 is way to low for small seeds and or any stage of the plants growth . i like mine up 50-60% for the 1st few weeks then try keep it in the 45-50% range with a max of temp 28c lights on 19c ish off

distilled water is kind of bad for a plant. i have not used it my self but because its stripped of most or all minerals you'll need to at least add cal mag to it around 150-200ppm or around 0.4 ec

adding cal mag to the distilled water will act as a buffer helping to keep your ph stable 6.8-6.4 soil use a higher ph 6.4-5.8 coco or hydro

i don't grow organically and i have not used Nature's Care Organic and Natural potting mix but from what i know yes that should contain the necessary nutrients for seedlings up until the i would say 3 ish weeks of veg then you'd top dress with a mix of 444 plus some sort of calcium and magnesium and what ever else organic growers use

the led grow light you are using has a bloom and veg switch im guessing. turn them both on the entire grow veg and flower and keep the light around 32 inches for now until shes looking better then go to 28inch. the reason i say turn both switches on is because of spectrum. yes plant don't really use all that much red in veg but its still will be absorbed also with the light being week in power the more you can get from it the better

do you have an extract fan and a carbon filter sucking air out of your tent and in to a different room or out the window. if no then you'll need to get that

i don't know how much electricity cost in your country but running a ac and humidifier or dehumidifier for a small grow is a big waste of money and electricity that could be put in to more light BUT if you cant keep temps and humidity in check and its the only option then i guess thats what you must do

im aussie so temps here are stupidly hot in summer and i find no matter what i do except add a ac i cant keep temp low enough. so i only veg over the hottest part of the year or stop for 2-3 months

by the way why are you using distilled water . is your tap water hard ?? if not just use your tap water

im not telling you what to do nore do i claim to know this is your problem but if that was my plant i would stop using distilled water. feed with some liquid cal mag and some epsom salt get my humidity up in at least 50% get my temps down to no more then 28c or abit lower

i dont think your plant would need a topdressing yet so id just try the cal mag and epsions both are fine for a organic type grow

at the end of the day you dont have to be all that fussy with being perfect just try keep stuff in range. ph and feeding correctly is more impotent to get right. this is why i prefer hydroponic type grows. you can keep ph and ec in range with out any of the guess work evolved with organics. i think if you want organic grow outside but i understand why people like to do it

i hope your plant grow out of her spots

[DirtyChai]

Thanks for all the good info!! I would agree with you that our humidity and temperature is an issue, however, this is the first I'm hearing of possible complications with distilled water. We'll definitely experiment with tap water, cal-mag, epson salt, etc. And turning on the bloom switch. Thanks again for the knowledge!

[Rwise]

Please research using distilled water as it is NOT PH neutral, it is acidic and causes low PH issues, which is what your plant is saying.

[Acology]

most people will use reverse osmosis water not distilled but both need about 250ppm or around 0.4ec of cal mag added before adding nutrients to the water or adding it to your soil

epson salt is a good form of readily available magnesium but you need to get the stuff that has nothing added to it like fragments very cheap stuff though and a small bag lasts a long time

ill add 1 tea spoon to a gallon of water once a month

do you have a ec meter or ppm meter and a ph meter