MPrudent

Seachem makes an alkaline buffer and acid buffer that alot of people have had success with. They also make a product called equilibrium but that is more to replace minerals and increase GH when using RO water.

aquarist48

Good morning. pH levels will fall over time. Here is a link you may find helpful. Enjoy your tank!
http://www.ratemyfishtank.com/articles/107

Nate McFin

Nice info Mprudent!
Not much to add regarding the Kh/GH/Ph triangle. They are very intertwined. Plants will eat up the minerals in water pretty quickly. If you water is soft then you will have Ph drops. My Kh and Gh are very low and my Ph after off gassing the Co2 is 7.5. My Ph will drop to 6.4 within a week due to the plants using up the buffer.
Crushed coral really seems to help.
The only other thing to add is.....you said you wanted some drift wood. driftwood will lower the Ph of your water as well so be careful there.
Best Wishes,
Nate