What fertilizers/supplements next?

Something is wrong with your soil mix............a plant this age and size should not need any extra feeding for at least 3 weeks or have any deficiencies if started in a quality and suitable soil mix to begin with. Mixing perlite, coco coir and clay pebbles is over doing it, you have "diluted" the soil goodness and have now turned it into a virtual hydroponic situation. Next time, forget the clay pebbles and only use either a bit of perlite, about 10% or about 20% coco coir in your soil mix,,,,,,,,,one or the other, but not both. It seems you could have a pH issue that is affecting nutrient availability or the soil you started with was very low quality with little to no goodness. Try giving your seedling some seaweed/kelp tonic in liquid form to the root zone to help it bounce back, then start in about a weeks time with some quarter strength cannabis specific "grow" type fertilizer, again, applied to the root zone. Foliar feeding/spritzing plants is pointless. You will also need to check the pH of your soil mix, aim for somewhere between 6.2 and 6.6. If your pH is out of range, this will affect the plants ability to access the nutrients in your soil mix. With the amount of inert ingredients in your soil mix, you may also need to start with a cal/mag supplement soonish as well. Due to so many inert ingredients in your soil mix (pebbles, coco coir and perlite) you will have to liquid fertilize this plant for its entire life...........start with quarter strength grow fertilizer before moving to half strength in about two weeks and then two weeks later, move to full strength if your plant can handle it. You will need to follow a schedule of plain water/fertilizer/plain water/fertilizer etc. Water/fertilize until you get some run-off (water coming out the bottom of the pot) then do not water again until the top inch to inch and a half of the soil mix has dried out............stick your finger in the soil mix to gauge this. Also, fill in your diary with every bit of information you can, often it is the little details which can pinpoint an answer.....without all the pieces of the jigsaw, formulating answers can be guesswork if not all the facts are presented.

Wait another 1 to 2 days. Give only water with an adjusted pH value. Once the plant is a bit stronger—in about 2 days—you can mix your nutrient solution according to the feeding schedule. At this stage, I always apply the fertilizer with a spray bottle.

Plant is sick. I would invest time to make grow plan, before i start growing. In my personal opinion - coco and soil mixes is wrong way of growing. Your plant state could be caused by wrong ph, lack of food, too intense light and so on....