Whats going on with this seedling?

Ive got 2 seedlings being given the exact same treatment, both same genetics, both th same age and yet 2 weeks in and one of them looks like this.

Ph issues?

It would be easier if we could compare it to the healthier ones, do you have a picture?

I had a green Gelato which did a similar thing, but it also looks like it's not got a reason to stretch. Are both this short? I also found that some of my strains had what I refer to as a "pause period" where some just have a slow growth phase inexplicably during the grow. One thing I did attribute it to was whether or not you've reported? Seeds I repotted never have the pause period and those I sew straight into their final pots seem to.

I don't know if this is consistent with anyone else's experiences, but its what I've found in my journey so far.

Good luck with the rest of your grow!

I sowed them straught into final 10l pots, no repotting, literally the being fed the same mixture same soil types and ratios, practically as close to being in the exact same loctation in terms of light humidity, airflow but one has responded amazingly, fimed yesterday

Some grow info could be helpful. Are you in soil? What kind? Did it already have nutrients? Etc

Looks like coco to me.
More info is required.

Coco and perlite, bit of myco, fabric pots, 600w led, the coco has been resued but it was treated prior to potting, rinsed, buffered etc, been watering just a mix of rhizo and cannazym with the occasional dip of calmag but i just moved them both onto veg nutes, low dose 1.5ml a + b per 5litres of water. Ph down to about 6.0, theyre both getting 2.5 litres run through them every 2 days, waiting till the surface drys out on the coco, im using fabric pots, run to waste. Recommend flushing through and continuing with water for a couple days? Or can i run the course with nutes, they are 15days up from germination

I think it's either the Pause Periid thing I mentioned, or its just that a 600w isn't really enough. I thought I was cooking on one 600W led, but was only pulling something like 5-7k lux. Compare that to outside which is more like 28k+ lux. You can use your phone sensors in an app to measure the lux in your grow area, maybe it's a place to start?

Feed coco daily to run off.
Never plain water.
Never let it get dry.

Pretty simple stuff.