New grower with questions about burnt tips, browning/scrunching leaves and some pale/yellow spots!

Most likely over feeding or the soil is to hot/salty. Give it less feed and ensure your getting runoff with each feed. I tend to like a good amount of perlite in the mix when growing with soilless substrates like coir or perlite. I see in your diary you are using rehydrated prefertilized coir. I think is the main cause of your issues. Coir I tend to rinse first use as it can hold onto a lot of salt from its processing. Out of the bag/block it can sometimes have a charge of around 1EC or 500PPM on the 500 scale. 500=1ec in shot. Also if you using a lesser brand of coir, it will not be buffered and will leach all the Ca and Mg out of the feeds and release excess Na and K. Need to add in Ca Mg on every watering and get runoff to prevent buildup. Give it some more water and it should be ok and recover just fine. Look at what you are feeding the and use a EC/PPM pen to judge how strong the feed is. I really like coir but it can take a bit to get used to its pitfalls. no medium is 100% perfect. and definitely look into mixing in about 20-30% perlite in the future.