Aquarium is a logic puzzle on a grid divided into bold-outlined regions called aquariums. You fill each aquarium with water from the bottom up so that every row and column holds exactly the number of water cells shown by its clue. Water always sits level within an aquarium and never floats above an empty cell in the same aquarium.

How do you start an Aquarium puzzle?

Start with clues only one height can satisfy, often the smallest aquariums or the shortest rows and columns. Confirming one height clears every cell that aquarium touches, which tightens the clues on the rows and columns it crosses and opens up the next deduction.

Is there always exactly one solution?

Yes. Every Puzzle Lair Aquarium puzzle is generated and verified to have exactly one solution reachable by pure logic. Being stuck means there is a deduction you have not spotted yet, often a cross-reference between a row and a column or a height limit you have not applied.

What does Check do in Aquarium?

Check tests your current board against the solution and reports whether it is fully solved. Marks give no live feedback as you play, so you can fill and clear water freely and press Check whenever you think every aquarium sits at its correct level. There is no mistake limit.

Why can two aquariums hold water at different levels?

The level rule only applies within a single aquarium, it says nothing about how one aquarium's height compares to another's. Two separate aquariums in the same row can sit at completely different heights, one full and one empty, as long as each aquarium's own rows stay internally consistent.

Solving guides

From the rulebook

How to Solve Aquarium

Aquarium is a logic puzzle played on a grid split into bold-outlined regions called aquariums. You decide how high the water sits in each aquarium so that every row and every column holds exactly the number of water cells printed along its edge. Water always settles flat and never floats, which turns each aquarium into a single number, its water level. This guide takes you from the rules to the techniques that crack hard grids without guessing.

Play Aquarium

The rules of Aquarium

An Aquarium grid is divided into bold-outlined regions, each one an aquarium. You fill each aquarium with water from the bottom up, or leave it dry. The numbers along the top and side of the grid tell you how many water cells belong in that row or column.

Two physical rules govern how water sits. Level, within one aquarium, a row is either entirely water or entirely dry, never partly filled, even when the aquarium bends into separate arms. Gravity, water fills from the bottom of an aquarium upward, so a water cell always has water beneath it in the same aquarium. Together these rules mean every aquarium has just one degree of freedom, its water height, whether it fills three rows, one row, or stays empty.

Read the row and column clues

Each clue outside the grid counts water cells, exactly like a row or column total. A clue of 0 means that entire line is dry, and a clue equal to the row or column length means every cell in that line is water. Every other clue narrows down which aquariums are filled in that line and to what height.

Because gravity pins each aquarium to a single height, a clue does not just tell you how many cells are water in a line, it tells you how the aquariums crossing that line divide up those cells. Reading a clue means asking which combination of aquarium heights adds up to that exact count.

Pin a height directly from one clue

The fastest opening move is a clue that only one height can satisfy. If an aquarium is the only one occupying a row or column, or if the arithmetic only works one way, that aquarium's height is fixed immediately. Small aquariums and short lines are the easiest places to find these direct hits.

Once a height is pinned, mark every cell it implies as water or dry. A fully dry aquarium clears every one of its cells at once, and a fully flooded aquarium does the same in reverse, both of which often finish off the clue for that line.

Cross-reference rows and columns

When no single clue pins a height outright, compare a row against the columns that cross it. If a height forced in one line would push a crossing line's clue too high or too low, that height is ruled out. Working a clue from both directions at once is how most Aquarium deductions actually land.

Watch for a clue that is already satisfied by the aquariums you have confirmed so far. Once a row or column reaches its full count, every other aquarium touching that line must stay dry at that row, since no cell in that line can hold more water.

Use height limits to rule out water

An aquarium can never hold more water than the rows it spans, so a clue that looks generous is sometimes impossible for a short aquarium to reach on its own. When an aquarium is too short to satisfy a clue by itself, its top rows stay dry no matter what, and you can exclude water there immediately.

Apply the techniques in order. Pin the direct hits first, clear the aquariums that arithmetic already decides, cross-reference every row against its columns, then use height limits to trim the rest. On Puzzle Lair every Aquarium puzzle is guaranteed solvable by logic alone, so if you are stuck there is always a deduction waiting, never a guess. Aquarium is currently marked beta, so rules and tuning may still change as the puzzle is tested.

Work through a small example

Picture two neighboring aquariums, each four rows tall. The left one sits under a column clue of 4, its own full height, so it must flood completely, all four rows filled with water. The right one sits under a column clue of 1, too small to reach with anything but its very bottom row, so mark only that bottom row as water and leave the three rows above it dry.

Now check the row clues those two heights create. A row totals 2 wherever both aquariums are still flooded that high, and a row totals 1 once only the left aquarium remains filled. Matching each row's printed clue against what the two heights actually produce is how you confirm a deduction before moving on to the next aquarium.

Frequently asked questions

What is Aquarium?: Aquarium is a logic puzzle on a grid divided into bold-outlined regions called aquariums. You fill each aquarium with water from the bottom up so that every row and column holds exactly the number of water cells shown by its clue. Water always sits level within an aquarium and never floats above an empty cell in the same aquarium.
How do you start an Aquarium puzzle?: Start with clues only one height can satisfy, often the smallest aquariums or the shortest rows and columns. Confirming one height clears every cell that aquarium touches, which tightens the clues on the rows and columns it crosses and opens up the next deduction.
Is there always exactly one solution?: Yes. Every Puzzle Lair Aquarium puzzle is generated and verified to have exactly one solution reachable by pure logic. Being stuck means there is a deduction you have not spotted yet, often a cross-reference between a row and a column or a height limit you have not applied.
What does Check do in Aquarium?: Check tests your current board against the solution and reports whether it is fully solved. Marks give no live feedback as you play, so you can fill and clear water freely and press Check whenever you think every aquarium sits at its correct level. There is no mistake limit.
Why can two aquariums hold water at different levels?: The level rule only applies within a single aquarium, it says nothing about how one aquarium's height compares to another's. Two separate aquariums in the same row can sit at completely different heights, one full and one empty, as long as each aquarium's own rows stay internally consistent.

Ready to play? Start a Aquarium puzzle