I use only Mopani in my tanks. It sinks right away with no soaking, its got awesome multi-color grain patterns & it never rots. If you don't want tannins, you will have to boil it for several hours. I always boil mine anyway, but I keep some of the tannin because its good for my water & fish. The water turns a beautiful gold-red with mopani, but other wood types just turn it brown. Petco is usually the cheapest for mopani at 7.99 for small chunks. Petsmart charges like 12 bux for the small ones.