Auto Widow

Yes this is normal. It takes awhile to get the bucket to stay on point. You can use something with humic acid in it like floricious plus and it will stabilize your pH for you. BUT it will also stain your roots brown. Set your pH to 5.5 let it drift to 6.5 and check the pH everyday and set it back to 5.5 over a week or 2 you'll get it to stabilize without floricious plus or anything else. I honestly did a comparison and floricious plus helps the pH alot, but I hate how brown it stains your roots. Stay on top of it and adjust it every 24 hours without and humic acid to regulate it, most of it's in organic form and it's just dark stuff. Also make sure your letting your tap water sit for 24 hours to evaporate chlorine or you'll never get the pH to stop fluctuating

No you shouldn't top an auto. Some lst is ok. Your system for veg should be set at 5.8 for veg cycle and 6.2 or 6.3 for when their flowering. Your ec level for an auto sits about 600 ppm 1.2 ec and that is pret near their limit on feed. With photos you can take them to 800 ppm 1.6 ec. But autos don't like as much food as photos. Cheers