man, here's my story, I was getting crazy about ph in my soil. Everytime I got some yellowing of leaf necrosis or chlorosis. BTW my tap water 8.5-8.8pH. I was making it more acidic, to be somewhere in 6.2-6.8. But later on I took Kite High advice. Then I read a book, other experienced growers threads. Time and efforts were wasted. pH in soil is rarely a problem. MJ is pH tolerant and soil has a buffering attribute and it fixes pH by itself. Read through
this thread only 3 pages, but there lies your answer to pH control
So after I quit upping or downing my pH, I did not notice any difference in my grow.
do not know a lot about 707, but from what I read it's quite light nuted, I'm really surprised how you are going without any nutes.. those would help you establish bigger foliage, root mass etc.. otherwise you are not going to yield much...