i think i read somwhere that if its a large section of it then it will lower ur ph... iv got a nice big chunk in mine an my ph hasnt moved....at all...
It depends how much you have of it and how well prepared you have made it before putting it into the tank. The misconception is all you need to do is wash when you get it home and then put it into the tank. If you do that two things will happen. Your water will turn brown and the water will turn acidic.
MP wood takes a lot of preparation time, that is why it's so cheap. Firstly you need to boil it for at least an hour in salted water. This will kill off any unwanted beasties that my be lurking in the woods cracks and crannies. It also serves to bring out the colour of the wood. (leeching) Once this has been done you then need to put the piece of wood in a bucket of water fully submerged for at least two weeks, changing the water at regular intervals. Once the water becomes clear, boil the wood once more and then it's ready for your tank. No changes to Ph no staining of water. Simple!