Actually I purchased this large driftwood and another one from the Aquarium Driftwood in Mobile, AL. They were already prepped and ready for use in fish tanks. They sank without any help. This particular one I am having a trouble with was used in my borellii growout tank for a year, but it was really too big for the tank (stretches all the way from one end to the other). Borellii loved it but I had a heck of a time cleaning the tank and catching the large fry.
After it dried up, it does not sink anymore (soaked it for weeks) and it leaches something more than just tannin into the water column. I suppose it is full of bacteria since, believe it or not, the night time respiration of the plants, bacteria and all living things in my planted 75G tank pushed up the CO2 level to almost a lethal level. I found all my fish floating belly up one morning when I inadvertently left off a bubble wand after a water change the night before. I checked the CO2 level and found it to be extremely high even though my CO2 system was shut down.
Anyway, I suppose I can boil the wood to kill off most of the bacteria on it, but I wonder if this stops the decay of the driftwood.