Aquarium アクアリウム

Aquarium is a logic puzzle about water finding its level. A square grid is split by thick borders into irregular regions called tanks, and you decide how much water each tank holds. Water behaves as it does in a real container: inside one tank it settles flat, so a filled cell means every cell of that tank in the same row is filled, and everything in the tank below that row is under water too. The numbers along the top and left edges say how many filled cells each column and row must contain.

Aquarium is not one of the classic Nikoli types. Its standard rules text is the short statement on puzzle-aquarium.com, which offers 6×6, 10×10 and 15×15 grids at Easy, Normal and Hard plus special daily, weekly and monthly puzzles. The mechanics combine line counting, as in Battleships, with region shapes: you count cells along rows and columns, but the tank outlines decide which cells rise and fall together.

On LogicPuzzles.io you get a new daily 8×8 Aquarium and unlimited 6×6, 8×8 and 10×10 grids. Every puzzle is built by a generator and then verified by an independent solver, and only grids with exactly one solution reachable by deduction alone are kept. The board checks your progress as you play and lets you mark dry cells with an ×.

Think of each tank as a stack of levels rather than a set of cells. A level is all the cells of one tank in one row, whether or not they touch, and it is always filled or emptied as a unit. The water in a tank is described by one number, how many levels from the bottom are full, so a U shaped tank behaves like communicating vessels.

Start with the extreme clues. A row clue of 0 empties every level in that row, and because water cannot sit above air, every level above those in the same tanks is empty too. A row clue equal to the grid width fills the whole row and forces every lower level of those tanks under water. Columns work the same way: if a column needs water from a tank, the lowest cell of that tank in the column fills first.

Next, compare clues with level widths. If a tank has three cells in a row whose clue is 2, that level stays dry, and so does every level above it in the same tank. When a row still needs a certain number of cells, list the undecided levels crossing it and check which combinations of their widths add up to the remaining count; often only one combination works. This subset sum reasoning is the heart of the 8×8 and 10×10 grids.

Common mistakes are filling part of a level, forgetting that a filled level forces every lower level of the same tank, and treating × marks as water. Use the × to record levels you have proved dry. A clue turns grey when its line is satisfied and red when it holds too much.

Aquarium is not a Nikoli puzzle, and none of the sources used for this page credit an inventor. The rules wording that other sites paraphrase is the one published on puzzle-aquarium.com, part of the puzzle-*.com family of browser puzzle sites that also serves Nurikabe, Masyu, Shikaku, Light Up and other types. Its settings include an option labelled Auto flood water and air, which fills a whole level and everything below it when you fill one cell, and marks the level and everything above it when you mark air. Row and column counts are also the core clue of Battleships puzzles; what is specific to Aquarium is the level rule inside each tank, which turns every tank into a single waterline to find.