yikes. im no expert at this as i am just a noob, but i have seeded lots of seeds so far. i found this yellowing/burning occurs in seedlings for a number of reasons. 1)u add nutes too early (i know u havent but i just thought i would include this), 2)the soil is too hot- to rich in nutrients for the plants, 3)the plants dry out too quickly either from underwatering or too hot of a growing area. #3 is how i just recently fucked up some seeds. got too hot, now they're all yellowed and losing leaves- but they were bag seeds already so maybe bad genetics. anyways, like i keep saying- make sure your soil isnt too strong!! honestly, use the shittiest soil you can find. like the cheapest one in the store, quite often a potting soil made by the store. if you arent able to water them super often, keep them in a gardening tray with a dome over them. my newest seedlings are in there with some clones of mine, and they are looking great right now! so try that.....