Today is the third week since I popped them in water. I have only feed just water at the moment no nutes. I will start with Canna coco a and b and rhizotonic at half strength and see how they react. Also added a humidifier but turned it off because it seems to over water the plants. when I have it on the plants droop not sure why. But all good for now.
They not small at all pal. You can't judge a seedling by size for at least the 1st 14 days have passed then you'll know for sure if they are slow. To me, they look good.
Your RH is little low. I find that if I wet a bath towel and hang it from the top bar at the side of the tent. As it dries it'll bring her RH up 2 70+%.. but as I said. They look on track.
Enjoy the rest of your grow.