hey guys, sorry i havnt posted on here for a bit. my bluetooth dongle for ma comp broke so i couldnt send pics. as it goes i found 1 on amazon for 1p.... BARGIN!!!!!!!! any how its day 19 now and my babies are still going

they are about 3-4 inch now and i watered them with 1/2 strenth nutrient solution yesterday. the yellow that started to appere on one of the plants after a few days has stopped now thank god. but...... i have another problem i think. the leaves are curling a little although there is no yellowing. any help would be very appreciated....... sorry about the picture quality, i am using a mobile phone to take pics.