Added a piece of dry pear tree wood to a 10gal tank, next morning Honey Gouramis eyes were bulging and nearly dead from either PH shock or some type of Tannin acid leached from the wood. Very bad mistake! Do not make this same mistake and add dry wood without pre-soaking it. Immediately did a full water change, added some extra air to water to keep fish alive, took about 10 hours for fish to recover. Hopefully I did not harm the fish permanently. Doing ok now. Will not be adding this piece of wood back in.