flush?

Hey all, I found out my leaf issues is most likely due to having a fooked up ph pen... it was reading about .8 higher than it should. I got a new ph and have tested my run off which is 5.1. I am growing in coco so would like this to be atleast 5.5! What would you do to correct this? Pic of leaf...

Hi, I am not anywhere near flush time.. But want to be sure I have that entity clear .... I am growing a large scrogged single girl in a 20l res. I am feeding her Canna Aqua and the rest of the main CANNA nuits.. Ie: Vega A B Florez A B Rhyzo. Zym, 13 14, and Boost.. and may add an additive...