Seed culture with no acidity after Phase 4 - how to proceed?

I'm following the seed culture instructions in Reinhart's Artisan Breads Every Day, aerating 3 times a day and feeding as directed based on fermentation.  Using Pyrex measuring cups to monitor growth.

5/20 p.m.   Started Phase I with rye flour and juice from a newly cut pineapple.  5/23 a.m. started Phase 2 with half whole wheat/half bread flour & cold pineapple juice from Day 1.  5/26 10 a.m. had robust bubbles and foam, and started Phase 3 with half wheat/half bread flour & bottled water.  5/26 4 p.m., after hours of bubbling (and doubling each time after 2 aerations), using 1/2 c. culture I started Phase 4 even though it was less than 24 hours - the instructions say it's OK to do so.  5/26 at 8 p.m. it had more than doubled twice after 2 aerations.  As of 11 p.m. bubbling has slowed down but is doubled again.  The book says Phase 4 takes 4-24 hours to become fully active.     

This culture seems to be quite potent and working as described in the book.  However, as of now there are still no signs of acidity on pH testing.  I tested the paper with apple cider vinegar and got the correct color, but my culture doesn't change the color beyond showing the paper to be damp (same as water).  The paper is off a new roll from my compounding pharmacist.  Based on fermentation activity the book says to proceed with turning it into a mother starter, but the pH says otherwise.  What to do?  Leave it at room temperature vs. put it in the fridge, aerating and wait for the pH to be correct, or move on now to the starter phase?  I live in the Monterey Bay CA region; cool nights but 70 during the day - culture is on kitchen table, away from heat.

Would using extremely fresh pineapple juice vs. canned/bottled be a factor?  Thank you and Happy Labor Day!