well well what is going on here i guess the whole world is wrong bout P H but i don't think so ....  i used 6.3~6.8 when i used soil with no problem and hydro 5.6~6.1 no problem i don't think who ever said 6.7~6.9 is full of shit go 2 your feed chart but then again there wrong 2 !!!!!!!!!!!!!!