I have a hard time keeping my PH above 8.12 alk is at 9.6 dkh and ca is between 400 - 440 may alk is a bit high but not much some salts have higher and some lower so I am ok at 9.6. I would check your tape water and get some crushed coral sand in there this will help buffer the PH a bit. oyster shells work also put some in your sump after making sure they are clean and sterile.

Bill