If these plant's are only 16 day's into flower i will eat my hat,But when flushing just get some water out of the tap and you can ph it to the same ph has yr feed is then just keep pooring onto the grow medium till the water run's clear.But i just flush with water straight out of the tap wait for the water too run clear then leave till water stop,s trickleing from the bottom of the pot's,then i follow this with a fresh made nute mix.Before anyone says it i have been doing this for years and never had any problem's,Flush and feed i first found out about doing this of a grower in holland and has long has the old nutes have been flushed there is no need to let the plants go without valuble feed time........................tyke.......................................