Ph imbalance? How to fix?

A soil pH of 6.4 is ideal. You have a developing cal/mag deficiency. Add a cal/mag booster to your fertilizer line up.......brown spots = lack of calcium........yellowing parts = lack of magnesium. Remember too.......what is showing in the leaves now, is a direct reflection of what was occurring in the root zone 2-3 weeks ago. Yellowing should recover in 10-14 days, but brown spots will remain, however the spots will not harm the plant or cause any isssues with growth rates, potency, overall health etc., so no need to remove the leaves just because they look "ugly". Add the cal/mag to the soil/roots, foliar feeding is generally ineffective for this issue. You may also want to add a soluble "trace element/mineral" mix (available from any decent garden centre) to your line up, a dose once a month will help with overall plant health and vigor. Although you are using "micro", I personally feel that product is missing a few essential extras that plant need.