Only yellow tips and curled under (pics)

Hi guys,

Recently sorted my other problems, I just repotted and slowed down on the watering. They have now thrived. Gone from 10 inches to 16 inches in a week.

One problem in the new pots is that the leaf tips yellow and curl under....

I have only ever gave them half strength high nitrogen nutrients ONCE about 2 weeks ago & only what was in the soilmix (worm castings). On week 4 of vegging 20hrs/4hrs

Is this a magnesium deficiency? There are no other problems, no bugs, pests, or brown spots or anything. Just this tiny yellow tip and curling under.

Pics below.
Many thanks.

That looks like bute burn from the pics I have seen I believe flushing would be the best thing at this point.

a slight nute burn . never be afraid to flush and renute your plants. remember less is always best, dont over nute cause you think its lacking something.
and make sure your PH is in the comfert range of 5.5-6.3 no more no less, this will allow your plants to readily absorb the nutes.

Watered thoroughly yesterday for the first time in 6 days. The problem is now rapidly disappearing