There is a PH Down chemical you can use. I used it one time that I messed up and it hit about 8.9. Lost a tang but was able to save the rest. I would use it and then test again. IMO I would do water changes instead of chemicals. The only reason I used it was cause how high it went within mins. A pretty good water change should get you where you want. You may be ok at 8.5 and let it go down on its own and stop dosing till it does.