What in the heck is going on

Ok so iv been growing hydroponicly for just about 3 years and i have never seen a plant do this i have used the same methed over and over for the 3 years the only things that have changed have been the following

1 new house iv never grown in

2 switched from led to cmh lights (dont think this is my problem)

3 first time growing autoflower

My tent stays about 73 pikes at 75 during the day

My ppm is about 300

My ph is around 5.8-6.0

Im using gh flora series nutrients
I do have hard water so im using the hard water flora micro hard water

What in the hell is going on with the plants

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What are those cubes in?

There in a humidity dome (propagation dome)

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Im thinking its nitrogen problum buy idk for sure

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Is that a burnt tip in pic #2?

Yes its from the first feeding iv sence diled the feeding back to 1/8 strength ppms about 300

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That is the only one that reacted to the 1/4 straight feeding

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Do you usually go from seed? I usually don't do nutrients yet at this point, they look very young. They come into the world with nutrient stores so nutes aren't needed for a while. Is your tap water 300 ppm or is that what you're feeding them? What's your water at initially and any idea what's in it? I was under the impression hard water was over 200 ppm or something like that. I'm right on the cusp of hard water at 160 ppm well water and there is some accumulation in toilet bowls/bath tub. I would guess over feed. Know it sounds funny, but young plants from seed are finicky like that, more so than clones IMO. Also gotta ask even though you've been doing this a while- pH'ed the rockwool?

oh ya, and autos are especially sensitive to nutes. From my memory, they don't like heavy feeding even in bloom, not like regular plants. It's been years since i've grown any though and the game has changed a lot as far as genetics and yield goes so I could be wrong, or no longer correct that is

Come to think of it, I haven't brought anything up from seed in a year! Wow! I think I do remember with young plants straight out the seed only using a tiny amount of Calmag as food till they get some leaves on them or start to show they're hungry. Calmag will usually kick some nitrogen and of course calmag. It's amazing what plants will do with just water as you probably know. An issue could be with what's in the water too, maybe something or levels of it they don't like. I've also always run RO water so no experience with hard water, sorry. Hope an autoflower enthusiast pops in for you.

My tap water comes out about 270ppm very hard. i do let my water set for 48 hours with air stones and my ppm drops to about 250ish. My water temp is right at 66°f and i ph'ed my rockwool with distilled water for 24h. They are from seed 13 days old. so giving them nuts this early may have been a boo boo. im use to clones so i guess i feed then out of habit lol was not aware the autos where sensitive to feeding.

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Bro, those babes are still so young..IMO you don't need to be feeding them anything! Maybe a 1/4 strength dose of Tappin' Roots or Superthrive but yeah, looks like an N overdose to me.