are you placing that wood in it? Are they being kept at the authentic mid 8 PH or have they been introduced to a lower range? Be impossible to keep it up that high with wood in it! If you are keeping it high, and realy want the wood, ask your lfs if they have any spare crushed coral or coral sand you can have and pop in one of your filter compartments, i replaced my chacoal for my african tank, it will kepp the ph up at 8-5 ish, but if is kept at neutral then dont worry!
You probably already know just throwing a wiley old Malawi keepers 2 cents in!