Stored nutes will normally have a slight lowering effect. It also happens in rez type systems for the first 3 to 4 days.
I think I have read that the Megacop does not need to be adjusted, however I have always said that PH is the single most important thing in growing hydroponics so I would still adjust to at least 5.7 to 5.8 before use just to be safe. They would stay a bit more accurate if they were stored in a open air type setup when they could interact with their surroundings. Kind of the same principle of why fish aquariums stay where you set them.
The tops of your plants are the true indicator of where your food is, and to me they look damn near perfect. I’d make the PH adjustment and keep doing what your doing. If anything seems to change just let us know right away and we’ll try to get the fix in b 4 any real issues arise.