Just feed them more. After the stretch is completed plants typically require a touch of N and cal/mag. Your plants look fine except hungry. You say your pH level is fine, well what is it? Should be in the range of 6.5 - 6.8.
There is no need to flush unless there was an error in feed strength or something. Flush is just leaching the soil of the nutrients you put in there.
I would give those plants a week of 50/50 veg and bloom food.