Runts Muffin - Purple Punch

You shouldn't flush with plain water in Coco until the end. As it removes the Calmag buffer it has accumulated. What is your run off EC? Always feed with nutes in Coco just don't over do it with the EC. To drop pH I will mix my nutrients and drop the ph to 5.0 . A couple of feeds later it will drop. Your plants look healthy so I would worry . Run off in Coco is ok from 5.8 to 6.6. so you are not far off . Just lower the pH to 5.0 for a couple of days. (With nutes ) at a lower dosage if your run off EC is high .