Aquarium Puzzle

How to use the Aquarium puzzle

1. Pick a board size (6×6, 8×8 or 10×10) and a difficulty (Easy, Medium or Hard) in the controls above the board. The default size is 8×8.
2. Press New puzzle to generate a fresh board. Wait for “Generating…” to finish if it shows.
3. Tap a cell to fill its tank with water up to that cell’s row. Every tank cell in that row and below fills.
4. Tap a cell in the tank’s top water row again to drain one row.
5. Right-click the cell, or use the Air chip, to mark a cell as air. This also clears water at that height and above in the tank.
6. Watch the numbers. They turn grey when met and red when exceeded.
7. Press Hint when you are stuck. It highlights the cells involved and explains which rule proves the next step.
8. Press Check to see cells that break a rule or differ from the solution, shown in red.
9. When the puzzle is solved, the page shows “Solved in m:ss” and offers Next puzzle.

On a keyboard, the arrow keys move between cells, Space fills the tank up to the row, X marks air and Backspace clears a cell. Undo and Redo work with Ctrl+Z and Shift+Ctrl+Z (Cmd on a Mac). Print produces a page with the puzzle, its size, difficulty and rules, and Copy link gives you a link that opens exactly the same puzzle on another device.

Aquarium puzzle rules

The grid is cut into tanks, which are outlined areas of cells. Your job is to fill some cells with water so that each row and column contains the number of water cells it asks for. The number at the right of each row and the number below each column are those counts.

Water is level within each tank. If one cell of a tank holds water, every cell of that tank in the same row and in all rows below it also holds water. This means each row of a tank is either all water or all air. Tanks have 2 to 8 cells and often stretch over several rows. Roughly half the cells in a puzzle hold water.

How to solve aquarium puzzles

Begin with the three basic rules the site’s solver uses. The first is level: water in a tank cell fills every cell of that tank beside it and below it, and air empties every cell of that tank beside it and above it. The second is full: when a row or column already has its number of water cells, all its other open cells are air. The third is all: when a row or column has exactly as many open cells as water cells it still needs, all of those open cells are water.

For example, in the 8×8 Easy puzzle with seed 3, row 1’s number is 0. Row 1 already has 0 water cells, so every open cell in it is air. That makes row 1, column 1 air.

Medium puzzles need line techniques. Look at one row or column and, for each tank in it, count how many cells the tank adds at each water level it can still have. A level is ruled out if it puts too much water in the line even when every other tank adds as little as possible (tooMany). A level is also ruled out if it leaves the line short even when the other tanks add as much as they can (tooFew). Finally, a level is ruled out if its counts cannot be combined with the other tanks to make the number (lineCount).

Hard puzzles need one more step. Try a water level for a tank, follow its consequences through the rules, and if it leads to a contradiction, that level is ruled out.

Frequently asked questions

Is the Aquarium puzzle free, and do I need an account?

Yes, it is free. You do not need an account or sign-up. Your progress and settings are saved automatically in your browser, and nothing is uploaded.

Can I play the Aquarium puzzle on a phone?

Yes, it works on phones, tablets and computers. On a phone or tablet, the chips above the board choose what a tap does: “Water” or “Air”. A third chip, “Move”, lets you scroll a zoomed board instead of playing. Zoom out, Fit and Zoom in change the board size, and Fit is the default.

Can I print the Aquarium puzzle?

Yes. Press Print to get the puzzle on its own page, with its size, difficulty and rules. Tick “Print the answer page too” to add the solution on a second page. In the print dialog you can choose “Save as PDF”, and both A4 and Letter paper work.

Does every Aquarium puzzle have one solution?

Yes. Each puzzle is generated in your browser from a random seed and is kept only when the site’s own solver proves it has exactly one solution. That means it can always be finished by logic alone.

What happens when I finish a puzzle?

The timer runs while you play and pauses when the tab is hidden. When the puzzle is solved, the page shows “Solved in m:ss” and offers Next puzzle.

Can I sell aquarium puzzles from this page in a puzzle book?

Yes. Aquarium puzzles from this page are royalty-free for personal, classroom and commercial use, including KDP books, Etsy printables, Teachers Pay Teachers and print-on-demand. No credit is required. The only thing you may not do is copy the generator or the site itself to run a competing service; see the terms.

Related tools

• Thermometers puzzle: use it if you enjoy filling a grid by following clues about rows and columns.
• Kakurasu: try it when you want another grid puzzle built on counting along rows and columns.
• Star Battle: choose it for a region-based logic puzzle where you place stars under strict limits.
• Tents puzzle: play it for a grid puzzle where you place tents next to trees with row and column counts.
• Norinori: pick it for a region-based puzzle where you pair up cells inside outlined areas.
• Binary puzzle: use it for a grid of two symbols that must follow simple counting and no-three-in-a-row rules.
• Nonogram (play online): play it for a picture puzzle where the row and column numbers describe the shape to draw.
• All puzzles on the site: browse this list to find every puzzle the site offers.