the first round leaves that emerge from a seed are its stockpile of nutz the plant'll use up for the first 3 weeks of its life so if its around day 21 then thats not that odd bu if u added any plant food or nutz to the grow medieum prior to day 21 ish then u most likely burning them and a flush would be recomended other then that make sure ur not feeding them rough water and watch how much u water as well ..luck..