Clone Questions Please

I had 3 clones going pretty good but i was wondering at what age can i start to add a little food in there water?

i wait till there about 5 inches, but as soon as there rooted i add some maxi crop sea weed extract to there water and they take off in root growth and foliage.

I'm not an expert but I'll tell what works for me.
I put the cutting in plastic cups with coco in my plastic dome to start of course with distilled water. With the coco packed tightly I can turn them upside down and they fall right out of the cups. Once I do that and see good roots after about 2 weeks, I wash all the coco off and put them in my bubblers with 1/2 nutes, about 400-500 PPM. After 1-2 weeks, I go to full strength nutes. I don't ever remember having nute burn doing it this way.