Saltwater ph problem!!!!?

Im just beginning a saltwater aquarium. I bought 22 pounds of live rock and 20 pounds of carribasea live aragonite sand for my 20 gallon aquarium. Its been setup for 2 days now and the gravity is at 1.023 but the ph is at 7.8. I use reef crystals for my salt and the ammonia ia at the highest level and the nitrite is at 1.0. I even bought a additive ph buffer to increase the ph but after using it yesterday the ph has dropped from 8.3 to 7.8 so the buffer has proven not to work after initially raising the ph and now dropping it. What is the cause of the ph to be low and how can i permanently fix it?