I got some grapefruti deseil and blue dragon clones they are realtively doing well but AM conserned because they strated doing the same problem you explained...i think its the soil since i used this miracle grow soil i lost 2 clones and the others seem to be be sprouting good just on leaf will look droopy and tips start to curl downwards then that leathery look...but only after they get big the new leaves are good until the next set pops out..let me know how you solve this problem ive been fighting it for bout 2 weeks...hope to fix it soon...better early than later..