Burnt leaves.....How do I flush?

I have these 3 clones together in a 5 gallon bucket and have been on 12/12 for 9 days now....its starting to show lots of nice healthy bud sites but there are some lower leaves that are crispy and yellow looking (see pics)....I was told that the miracle-gro soil im using is really not the best for cannabis growing and that I should flush the soil real good....could someone tell me how to properly flush my girls and when to start fertalizing again so they can stay on track and produce nice fruit! Any advice is appreciated! BUD IS LOVE!
RHMH

i am not an expert on this but i have faced the same problem a few days ago with one of my plants as well....what you must do in my opinion is to seperate the plants into individual pots....since you claim that the clones show growth , this means that they have already roots.....
if that is not an option right now you can do what i did to save my plant.....i got the 2 gallon bucket in the bathtab.....regulated the temperature of the water to be warm, not hot but certainly not cold as it would affect the roots....then i pured into the bucket water, 2 times the size of the pot.....then wait for it to drain well....you are going to loose a respectable amount of soil in this procedure but trust me it is worth.....after that place the plants as centered as possible under the lights so as for the water that is left evaporates as fast as possible from the soil...use a fan as well to circulate the air and speed the procedure of evaporation.....i did this almost 12 hrs ago and i can see clearly that my plant is saved as it is greener that before and a little bit bushier....i know that sounds crazy but flushing it, lowering the lights (min safe distance) and using better air circulation, really can help you....or you can just wait to seperate them....anyway, that's all the info that i can give you right now as i am not an experienced grower myself...hope this helps you as it really helped me.....i have posted only because i can understand how much you think of your plants these days.....maybe someone else can input some advice of the watering issue....i guess though that you must not apply any ferts yet, maybe a few days later, when you are certain that your ladies have passed the danger.....do not know what signs will tell you that but i am pretty sure that you will know that as you watch them closely a few times a day as all of us do......hope that helped....