Hey! The other guys advice would be solid if you were running soil.
With coco however, there are no nutrients in it and coco holds lots of air which makes overwatering difficult.
Coco is actually a hydroponics medium so you really dont want it to dry out. You should water it daily at least. If coco drys out it repels and doesnt absorb water, making it very difficult to saturate all the coco when you water. This can lead to dry pockets of coco in the middle of the pot that will dry out and kill the roots. Also when you water you want to make sure to have 20% of the water you put in to run out the bottom of the pot to flush out any old nutes when you are feeding. Make sure your pot has tons of drainage as well and make sure to discard any runoff so the plant isn't sitting it in being overwatered. You dont want any water pooling in the bottom of the pot.
Another thing to note, you should have started feeding nutes once those first serrated leaves grew in. Since coco has 0 nutes in it, the seedling will eat through its built-in reserves quite quickly. So at this point you should start feeding nutes. Coco is also different from soil in that you need to feed every time you water or you will be starving the plant.
Coco also requires a lower ph level than soil and ph levels are extremely important. Coco likes 5.5-6.0 for ph. Too high above that and the plant just cant absorb a lot of the nutrients it needs for daily growth and it will pull them from its leaves.
Make sure your lighting isnt too close to the plant as well. The white leaf tips could be light bleaching.
Coco also sometimes comes with lots of salts in it because it comes from coconuts. Usually you need to wash it before use. These salts can burn the plant.
All in all it could be a few things. It could be light bleaching, salt burn, incorrect ph, or the complete lack of nutrients. I would start by raising the light a little and feeding nutes.
Hope this helps! Feel free to dm me if you need more help!