Unique aquarium decorations?

Thanks, he's an axolotl. The legos do float. I just siliconed them down to the bottom of the tank glass with aquarium silicone. You have to wait a few days after to let it dry and fully cure before adding water and sand again etc. I was worried about the little Hagrid minifig staying down since he is just attached to a flat lego brick thats siliconed down and he kept falling off it easily, but he's staying attached fine now that it's all in there.