You need to look at the pH issue in relation to what the EC is doing... I don't see that you're even monitoring/measuring the EC so that's going to be a problem. If you've got a ppm meter, it's easy to get the EC.. the equation is (ppm/1000)*2 ... and then it's going to depend on whether or not your plant is drinking (the water level is going down) ... if it is and if both EC and pH are rising, you need to lower the EC ... if the EC is stable and the pH is rising, that's normal unless the pH swings by more than 0.5 in which case you need to do a bucket change and lower the EC... if the EC is falling and the pH is rising, you would need to raise the EC. Now all of that changes if your plant is not drinking...
With that insane swing of the pH, I would recommend you do a bucket change... and I would also recommend you keep track of the EC... for an autoflower this age, you want an EC between 0.2 and 0.4 (which is basically tap water) and I'd be willing to bet that you've got a MUCH higher EC... So week 1, EC 0.2-0.4, Week 2 EC 0.4-0.6, Week 3 EC 0.6-0.8, Week 4 EC 0.8-1.0, Week 5 EC 1.0-1.2 and keep it at this EC for the rest of the grow...
Good luck...