no need to flush just back nutes off a lil and you be golden :thumbsup:
Flushing will only add time and effort, as already stated you can not undo what is already done. If you are topping off your res during the week with plain PH'd water and draining and refilling your res weekly then continue on with topoff during week and minor sdjust nutes on refill.
Problem solved ..... next :jointsmile: