If you use more tiles to make a number than there are bubbles to pop with that number, any extra tiles will fall to the bottom of the tank as rocks. This will add water to the tank and make the level end faster, so try to use the same number of tiles as there are bubbles showing with that number, whenever possible, to have more time to earn points and unlock all the fish.
Find more information in our PDF guides to the new Osmo Numbers app and Osmo Numbers Education (the original version of the app).
