Most wood will slowly but surely release things like tannic acid into the water, slowly dropping the pH. It's all a balance really, as if you have lots of coral or limestone then they'll buffer it up to higher pH's again.
thanks folks. Now i think i might try to add some driftwood in the bigger tank when i relocate the cichlids. knowing its just in small margins & i have over 100lbs of reef rock and sand that should keep it balanced. plus i use homemade pH Up to keep it around 8.0
New driftwood may produce tannis for a long time after putting it in the tank. Dont be suprised if the water turns a tea color. Water changes will remove the tea coloration.