The fluctuation is normal. Assuming you are monitoring alk and that is where it should be those ph numbers are good in my opinion. The primary reason to dose limewater is to help supplement alk and the side benefit is the ph boost. I would be concerned if it get much higher though. I recently decided to dose limewater (kalkwasser) to increase ph and my fluctuation is 8.25 ish during the day and 8.05 ish at night. Before that I was debating on a co2 scrubber but I'm happy with this for now and it's way cheaper than scrubber. You can always cut back on the amount you are dosing to reduce ph. I'm not sure what the alk demand is in your tank but you can also dose baking soda and that will slightly reduce ph if you still need alk.