I don't recommend the perfect PH
products as they ussually contain elements that cause problems in other areas (like phospate buildup).
Is it a fish only tank?
You might want to check to see if you need buffering (as reefrunner mentioned) and then perhaps get some Kent SuperBuffer. Be careful using this product too much can nail your PH
high and you'll never get it down so go slow and test often. Once set though you will notice that the PH
will become very stable and even adding acids won't cause a PH
bounce. Of course this is just another alternative to dripping Kalkwasser (chalk water).