Leaf yellowing getting worse

It looks like a minor or secondary nutrients deficiency, which are extremely rare, it more likely is lockout due to excess phosphorous and / or potassium. Try some flushing of the media

The Iron deficiency diagnosis is good , the solution is good too . The ph range diagnosis is good as the sweet spot in soil is 6.5 BUT I disagree with the "Optimal pH should be 7(neutral) or better 7.3 to 7.5 but not to high" because optimal ph in soil is in the 6 to 7 ph range so no worries in that range , better use the average 6.5 value to avoid any ph issue

Nvm I thought nobody answered. But you already have your solution.

if you are watering at 6.5 and the run off is 6.2 it means that the soil pH level is lower than the optimal pH of 6.5. The solution would be to water with a higher pH. When your run off pH level reached 6.6 or 6.7 you can start giving her the normal water whit a pH of 6.5. The run off should be also 6.5. If this is not the case, continue watering at a higher pH. Optimal pH should be 7(neutral) or better 7.3 to 7.5 but not to high. I'm also a new grower so please wait for different answers but I heard that soil shouldn't be so low pH.