3rd grow (Dialling in the basics)

Ignore the ml/l as I usually add bit by bit and use a ppm meter to check. I've been lazy documenting the grow. Strange situation occurring where each of the 3 pots is giving runoff at 3 different pH! One is 5.5 which seems like long term that will negatively impact on the plant. One is 5.8 which matches the pH of the feed I'm watering with. And the other is hovering around 6.2 which should be safe once it doesn't continue to drift beyond that.