Old leaves are old news, and usually don't recover. Pick them off the soil when the plant discards them. Other than that, I'd leave 'em alone. (don't want to add stress via trimming off the dying stuff)
Watch the new growth for any further problems. Changes can take a few days to a couple of weeks to notice improvement, depending on the severity of the issue. I wouldn't expect an overnight change, as new growth might still be showing stress for the next week. (usually ph issues clear in about a week)
Ph issues will lock-out nutrients, so doubtful you are burning the ladies...unless you've been upping the dilution rates in hopes of clearing-up the issue.

Might want to think about switching to 18/6 light schedule. Some folks disagree, but I'm a firm believer that cannabis grows better with a dark period. (healthier, fuller, happier )

I'm still not a hydro guy, so someone else will have to check your spray durations and times...and quantities of nutes. :thumbsup: