Aquarium

The grid is divided into irregular tanks. Your job is to add water to the tanks so that two rules hold: water in any single tank always settles flat, filling from the bottom up; and the amount of water in each row and column matches the number printed beside it.

Because water obeys gravity, a tank can't have water sitting above an empty cell within the same tank. Use the row and column clues to deduce exactly how high to fill each tank.

• Click an empty cell to fill its tank with water from that row downward.
• Click a watered cell to drain that tank from that row upward.
• Rows and columns turn green when their count is exactly met and red if you've overfilled them.

• Desktop: click a cell to raise or lower its tank's water level.
• Phone & tablet: tap a cell to set the water level, no keyboard needed.
• Use New Puzzle for a fresh grid or Reset to empty the current one.

• Daily, the same puzzle for everyone each day, at your chosen difficulty.
• Practice, endless fresh puzzles.
• Difficulty, Easy, Medium, and Hard use progressively larger grids.

• Start with rows or columns whose clue is 0 or full, those cells are forced immediately.
• Remember a tank fills as one body: deciding one cell's water level often settles several cells at once.
• Cross-check a tank against both its row and column clues before committing to a fill height.

Aquarium has no recorded inventor and belongs to the broad family of grid logic puzzles that divide a board into irregular regions and constrain them against row and column totals — the same skeleton as several Nikoli designs.

What makes it unusual is that one of its rules is a physical law rather than an arithmetic one. Water settles flat: within any tank it fills from the bottom up, so a cell cannot hold water unless every cell beneath it in that tank does too.

That single borrowed rule does most of the work. It means a tank is not a free set of cells but an ordered stack with only a few legal fill levels, which collapses an enormous search space into something a person can reason through — and it is why the puzzle reads as intuitive despite being, underneath, the same kind of constraint problem as the rest of the family.

Aquarium is a gravity-based logic puzzle in the deductive grid-filling tradition, solvable by pure reasoning with no guessing required. This is an original, free browser version with daily challenges and three sizes, no download or sign-up.

A free, original browser game on PlayPendium. No download, no install.