the leaf tips curling up is more than likely a magnesium deficiency that is being caused by you using RO water.

RO water has no calcium or magnesium micronutrients in it, so you need to add something like CalMag to the water to get those. You may already know that and may already be adding it... but with the given info thats what i suspect.

Is there any reason why you are using RO water? I;m assuming your growing in soil, and unless your tap water is very heavily treated by your municipal water workworks you should be fine with it. If you are concerned about chlorine in the tap water it can be easily removed by just letting the water sit in an open container for 24+ hours before giving it to the plants... all of the chlorine will evaporate in that time. If you are concerned with flouride in the water, there are tablets you can get to remove that too. Small mounts of either won't really do any harm though.

Anyways... as for if its safe to clone... honestly I don;t know with it having a Mg defiency, personally i'd play it on the safe side and get that problem fixed first.

As for what part of the plants to clone - basically you clone using a branch, not a fan leaf. A branch would be any part of the plants that has internodes on it (places where other branches and fan leaves come from).

everything else you want to know about cloning is covered here: http://boards.cannabis.com/basic-gro...-kush-mom.html