PH increased during primary fermentation

[KellysBane]

I attempted to find an answer to this question but have not been successful online. So I am turning to you guys for help!

My primary fermentation is complete and I tested my PH level with my PH tester and it went from a starting PH of 3.6 to now 3.9. Has anyone else experienced this and is this normal. This is the first time I have tested PH while making cider.

 

[gregbathurst]

That is normal, though maybe a bit bigger difference than usual. If your cider has gone through MLF it always goes up quite a lot, that doesn't mean yours has definitely gone through MLF but it may have done.

 

[KellysBane]

I let the cider come up to room temp and the PH adjusted back down to 3.6. Apparently the temp can affect the PH reading based on the thickness of the testers glass probe. so I then warmed it and tested again and it drop a tiny amount 0.1 only. Isn't science awesome!!
Anyways Ill be transferring it for its a MLF and add some tannins, any opinions on what to use, earl grey or oak?