Really....I don't believe you have a problem....when I water in a soilless mix my ph is 5.5 to 5.8.....and my runoff is 6.2 to 6.5 depending on what I am feeding.

all you have to do is add baking soda to your water and mix real good and it will raise your ph quickly.....at this point.....I really don't believe your problem is too severe