Lowryder #2: Leaves curling under

Hello there. I have been growing some lowryder #2 from seed, which are now in their 21st day. Some of the seedlings have had somewhat droopy leaves since they sprouted pretty much, which i put down to possibe over or under watering. Watering both less and more didnt appear to do anything to solve the problem, and now they are beginning to flower and the new growth looks both stunted and curled up. From the plant problems post it looks to me a lot like a zinc deficiency.
PH looks ok (around 6.8ish according to my not entirely accurate soil testing kit), so I added a bit of 0.02% zinc fertiliser yesterday, but there doesnt seem to be any improvement.
I also yesterday transplanted one into a larger pot to test, but that had no effect.
Dont know if its relevent, but the two without problems are growing perfectly using exactly the same watering+feeding schedule. All the plants are watered a small amount once a day, and are completely dry by next morning.

Attached are pics, hopefully someone can give me a bit of advice.
Thanks

It usually takes at least 4days before you'll notice any difference after you treat them. You'll rarely see results the next day. some plants just fade away for no apparent reason
I was just wondering why you put them in2 flower so early

i think lowryder is a autoflowering??? i could be wrong though

yep lowryder is autoflowering

Those are definitely over-watered. The method you are using to water them is not correct. You should be saturating the soil thoroughly, to the point where excess water begins to seep from the drainage holes. Then you allow the soil to almost completely dry out before repeating. If your temp and humidity are within the proper range, you shouldn't be watering more than once every 3-5 days. By doing it the way you have been, providing a little bit of water every day, the roots stay balled-up at the bottom of the container. They don't get enough oxygen because they are constantly in a wet environment. They don't spread out properly throughout the soil because all the water they require, and then some, is always available to them at the bottom of the container. And they end up tangled and intertwined, becoming root-bound. At this point, you should stop watering them. Leave them alone for about 4 days and give the soil time to dry up. When it is time to water them again, water them heavily with a little less than half as much water as the size of the container (i.e. If you are using 3gal containers, water each plant with 1 whole gallon of water). If you do this, your plants should perk up and look healthy within about a week.