how is your root system? I had a similar issue when i first started hydro. I eventually realized that because i was constantly messing with the ph that the root system had gotten dammaged. The roots became thick and lost the normal little fingers sticking off of them. As far as flushing hydro, I usually use clearex for sbout 45 min one time and that does it. You could have lock out from nut build up but it should only take one 3o min flush to straiten out. If your plant is still reacting poorly to fresh watter with 1/4 nutes then its prob root systme damage. good luck