What is going wrong?

hey! since this is really early and the soil looks really really wet on the pictures, i would guess that's the problem and that's why the plant is looking like that. You have really intense LED lighting on? Then that might be the reason the plant shows magnesium deficiencies, try using a calmag fertilizer. don't forget some fertilizers need quite some time until the plant can do anything with it. If you really feed 1.5 L of water for that small amount of a plant, then im sure thats the problem, you drowing the roots(water is in the soil for SO long, the plant can't absorb any oxygen) ant waterlogged (at least thats my opinion, good luck on your problem

The soil looks pretty damp and there is already a layer from watering. Do you got holes in the bottom of your Buckets ?

Hey growmie, that looks like a beginning of calmag deficiency although some might say it's too early at this stage to develop one. Interveinal cholorosis in older leaves might be a sign of this. I suggest trying adding some calmag with your next feed and monitor the symptoms. Also 3ml of algagrow per 1.5L sounds like a lot, I don't have Plagron schedules next to me at the moment but I highly recommend using 25-50% if the prescribed dosage for the first month at least. Autoflowers usually need much less nutrients. Good luck!