Bro,forget that runoff crap.everyone is confused about it I see. Do your plants look OK? Then there is no problem.higher runoff ph than input ph means your plants absorb the nutes well and this is a great sign.if ph was just like how you set your feeding ph then this would be a problem because all nutes that build up in your pots drop the ph dramatically. Runoff is shit bro,runoff is nothing unless your plants are dying. Coco makes the nutes more and always available to your plants than soil,they probably eat well,do not get confused on runoff please and do nothing about it. Yes,flushing with acidic water will make the runoff drop but this will most likely cause problems.better stay like this,do not mess up your coco please. If your plants grow well,dont take action.if they dont,please share photos with us so we can find a way to recover.
Trust me,your plants dont feel the way you are worried about them.
Do you analyse your urine every day or every month? I guess no. Doctors only ask for it when you are sick.think like this.