First grow

I try to stay within 10 degree difference

I would try and keep your PH at a stable 5.8 and only go up to 6.2 when you start to enter flower. If you notice that PH is drifting your plants maybe they are feeding more then expected. Have you been monitoring your EC of the feeding solution? Is it dropping a lot over 24hrs and does coincide with the rise in PH? You could try and do a flush to get the PH back to normal and then go from there, but before doing this I would recommend making sure the above values PH/EC are checked first. If you do not have a TDS pen I would suggest you get one. Good Luck!

Bubbling air into water will change the PH of the water. I made a mini graph of this and how it relates to using phosphoric acid as PH down on my one grow. It all depends what type of mineral composition is in your tap water. If you using an air stone in the reservoir or bubbling before adding into the pots it should not flux to much. One other thing to note as well, if the air your bubbling into the water is high in co2, it will form carbonic acid and lower the PH as well. My tap water went from a PH of 7.3 up to 7.9 after bubbling for only 40min. The control went from a PH of 7.3 down to 7.2 growdiaries.com/diaries/129773-grow-journal-by-m0use/week/704902 look at the last photo for the graph/results. I also bubbled the still water that I was using as a control at the end and its PH closely matched the bubbled one. I tested using 1L of water in clear glass mason jars. It was not a perfect test. I would have liked to test it over longer periods of time and see if it drops or rises from extended sitting periods. Put an air stone in your reservoir if you don't already have one. Good Luck!