Acid Pool is a game mechanic in Bloons Card Storm that adds a puddle of acid on a space of the Bloon track. The mechanic was introduced in version 4.0, but it was not considered a keyword until version 4.2.[fn 1] When a player ends their turn with an Acid Pool on their track and a Bloon occupies the same space as it, it deals 30 damage to the Bloon. Acid Pools last until they have dealt damage two times, and they become slightly faded after dealing damage one time. If a space already has an Acid Pool, placing a new one on the same space replaces the original. While Acid Pools deal damage after On Fire, if a Bloon is both On Fire and on a space with an Acid Pool and On Fire deals enough damage to pop the Bloon first, the Acid Pool still damages the Bloon before it pops rather than damaging the next Bloon. Contrary to what the description implies, they can last an infinite number of turns as long as they don't deal damage two times.
Strong Acid Pool is a keyword similar to Acid Pool, except it deals 50 damage each time instead of 30. Placing a Strong Acid Pool on a regular Acid Pool space replaces the regular Acid Pool, and vice versa. The only card with this keyword is Bloon Master Alchemist.
Left: Acid Pools