If it were me, I'd cutoff all rain water from the plant that has yellowing leaves, not sunburned leaves, thats a different issue. Then adjust the water I fed the plant to 6.3-6.5 PH and continue your normal watering schedule. After 7-10 days I'd compare leaf color to known healthy plant to check progress. The nutrients including iron are already in your soil, having the PH off prevents the plant from absorbing them.
My outdoor vegetable garden is fed 6.5PH water daily because my soil runs around 8.4PH. I adjust my water with distilled white vinegar purchased for about $3 a gal at the supermarket.
Get a decent PH pen to monitor your water.
I really like this post by Emilya, it may offer additional insight for you:
pH in soil and run-off too high