Don’t ever bring the PH down like that. It’s not good for the fish. Please don’t do it again. His PH is fine at 7.4. My bettas are at 7.6. If you want to lower a PH, add some Indian Almond Leaves and drift wood. We all made similar mistakes in the beginning. That’s how we learn. Just keep an eye on him. If he acts funny, do a w/c. At least it wasn’t a drastic change. PH fluctuates during the day. It can be higher in the morning and lower in the evening or vice betta. 