Great pieces of wood! My plecos love it.We got 2 pieces of medium sized and while they vary, one is perfect for our 39 gallon and the other works great in our 55 gallon tank. Which already has a previously ordered medium piece.I suggest ordering the 2 pack of medium for anyone with 55 gallon tanks for less. That way you get 2 options since they are all different.I would think a large would be far too big for anything less than a 55 gallon.Boil wood to leach the tannins faster. It took about a day on medium high heat and a few water changes. Then soak with room temperature water until its a very pale tea color.