when it comes to most pond fish, they like the PH to be slightly Alkaline.you don't have to be worried if the PH is around 8 any higher you can consider using PH down.
1kg present as sodium phosphate - Monobasic
directions for use
Use PH test kit to measure PH levels in ponds or aquariums, Add PH down periodically to the desired PH of 7-8.
All PH changes should be made gradually to avoid stressing your fish over the course of a week.