I use plain water to root the clones. If i let the clones only in water with low intensity light, they root but dont grow at all. Sometimes i let the clones in the water with indirect sunlight (and 2 h of a far 15w CFL in the middle of the night, to avoid flowering) for more than 3 months, and then i put them in cococoir with grow light and grow without any problem. Probably its possible to prolong this period with very light foliar feeding, but i never need to do it.