Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
Depends on the driftwood, too. Some seems to have almost no affect on the water chemistry, and little to no tannins.
Remove tannins before adding the wood to the tank. Boil the wood, or, if it is too large you could run a very hot shower over it, or soak it in whatever container it fits in (kiddy wading pool, garbage can, bath tub...) in many changes of water for as long as it takes (several weeks, a month) to reduce the tannins to where it is acceptable.
Best way to counteract the constant, low level of acidic reactions is to add coral sand, oyster shell grit, or limestone sand to the filter. I use a nylon stocking as a media bag. You control the level of change by the amount you use. Test and find out how well it works for you.
1) research the fish. What are their requirements? Most important is GH.
2) Test your tap water. How close does it meet the needs of the fish?
3) Test some of the water the driftwood has been soaking in. Is this better or worse for the fish you have in mind?
4) Add some minerals like baking soda (raises KH and pH) and Epsom salt (raises GH) to the soaking water. Does this help? For how long? (I suggest these easy things because you probably already have these on hand)
5) If the test 4 worked, try any of the materials I listed in the paragraph above. Coral sand is sold for aquariums. Oyster shell grit is sold for small caged birds like Budgies. Limestone sand might be common in your area, or you might have to go shopping in a masonry yard. These are slower, and probably will match the slow action of the driftwood in the tank.