flush ph water help

My plants are a little behind on their need for flushing, I am growing autoflower in FFOS and using Organic Earth Dust fertilizer. Does anybody know if i have to flush like people claim to do whilst using liquid fertilizers? Is it really just for taste reasons? And if so, what are some tips...

Can I flush with my water it comes in a bit high on the ph scale wondering if I could just use a ph down or should I buy a flush chem (newbie grower)