i saw the Green man feed the plants that were only 6 inch tall ,2nd week. full stregth nutes and in the first week half strenth..........why cant i do the same.........im a newB......
You just answered your own question. Because you burn your plants.
He knows what he's doing and has been doing it for a while. Are you using the same nutes, same amount of nutes, and same feeding schedule, on the same clones as ol' boy did in the video? If not then you don't know how they will react to it.
You're fine as far as size...it probably could be a bit bigger, maybe a foot tall or so, if you hadn't poisoned it from the get-go. However, it's only a couple weeks you can't expect much. You will lose time and size however, by having to flush it.
I'd flush for a week or a week and a half and if the leaves start to yellow then I'd hit it with a very low-dose N fert.
EDIT: Re-read your OP and had forgot you were using a hydro setup. Never grown hydro but I imagine everything I said would still apply, except for possibly the flushing. I'm not sure how long you should flush in hydro since you're only trying to flush the plant of excess salts, not the grow medium itself.