Omfg

start a diary, lack of information is not helping. When growing in coir you need to provide everything to the plants as coir is void of nutrients. It also need a bit extra supplementation of Calcium and Magnesium to help buffer the coir. If you using a cheep brand of coir it may have also needed a rinse to get rid of excess salts as coir is notorious to holding onto salts as the cheep stuff is rinsed with sea "salt" water. low EC for a sprout this stage. 0.5-0.7 then increase it 0.1-0.2 every week til you hit 1.4-1.8, autos are different and need a bit less. max 1.0-1.2 as well as the lack of aeration in the medium from your other questions. you may not notice it now on the other plants but if their root system get blogged down later in life you will notice something similar to this in their leaves and growth. its an issue with the roots not the leaves they are mearly showing the sysptoms.