Aquarium Puzzle
Aquarium gives you a grid divided into irregular blocks separated by thick borders. Each block is an “aquarium.” Your job: fill each one with water to the right level so the numbers along the edges are satisfied. The numbers tell you how many filled cells belong in each row and column. The catch is that water behaves like water — it fills from the bottom and stays level across the full width of its container. No floating puddles, no gaps below the surface.
Aquarium
6×6 — Small grids with 4-6 aquariums. Row/column counting and basic water-level logic handle most of it.
Standard play. Timer runs. Hints available.
What is an Aquarium puzzle?
Aquarium is a logic puzzle with an unusually physical feel. The grid is sliced into irregularly shaped regions (the “aquariums”), and you decide how much water goes into each one. Water obeys gravity: it fills from the bottom, and the surface is always flat across the full width of the container. That rule creates cascading deductions — filling one cell at a certain height means every cell below it in the same aquarium column must also be filled.
Unlike most logic puzzles, this one has a real-world analogy everyone understands. You don't need to learn abstract concepts like “connectivity” or “Latin squares.” If you've ever filled a glass with water, you already get the core mechanic.
The four rules
Every Aquarium puzzle follows four constraints:
- Aquariums are separated by thick borders. The grid is divided into irregular blocks. Each block is one aquarium.
- Fill with water or leave empty. Each aquarium can be filled to some level, or left completely dry.
- Water is level. Within each aquarium, water fills uniformly across its full width at any given height. There are no gaps below the surface — water can't float.
- Numbers tell you the count. The numbers outside the grid show how many water-filled cells each row and column must contain.
For solving techniques and worked examples, read the full strategy guide.
How to play
Each cell cycles through three states when you click or tap:
- Empty — not yet decided
- Water — filled (shown in blue)
- Marked empty — you've confirmed this cell is air (shown with an X)
Shift-click (or long-press on mobile) to mark a cell as definitely empty. The clue numbers along the edges update in real time, turning green when satisfied and red when exceeded. Keyboard shortcuts: arrow keys to navigate, Space/Enter to cycle, W for water, X for marked empty, Delete to clear.
How Aquarium compares
Aquarium sits at an interesting intersection of several puzzle mechanics. It borrows the row/column counting clues from Nonogram, the binary filled-or-empty cell state from Binairo, and the thick-bordered irregular regions from Suguru. What makes it distinct is the water-level constraint: the physical behavior of water within each region creates deductions that none of those other puzzles can produce.
The closest relative is Thermometers, which also uses a “fill to a level” mechanic with row/column clues. But thermometers are straight tubes (one cell wide), while aquariums are irregularly shaped regions spanning multiple columns. The irregular shapes make the water-level constraint much richer.
Origins
Aquarium is not a Nikoli puzzle. It doesn't appear in any Nikoli publication, and there's no Wikipedia article about it. The puzzle's exact origin is unclear — it seems to have been created or popularized by the puzzle-aquarium.com website, which is part of a network of dedicated puzzle sites. That site is the only other place on the internet where you can play Aquarium puzzles. There's no entry in janko.at (the largest puzzle encyclopedia), no Simon Tatham implementation, and no Conceptis page.
This content vacuum is unusual for any puzzle with search volume. For context, even niche Nikoli puzzles like Nurikabe have multiple dedicated sites, Wikipedia articles, and solver tools. Aquarium has almost none of that.
Difficulty levels
| Level | Grid | What to expect |
|---|---|---|
| Easy | 6×6 | Small grids with 4-6 aquariums. Row/column counting and basic water-level logic handle most of it. |
| Medium | 8×8 | More aquariums interact through shared rows and columns. Forced fills and empties become necessary. |
| Hard | 10×10 | Over/under counting enters the picture. Some aquariums have several plausible water levels. |
| Expert | 12×12 | Cross-constraint analysis across 144 cells. One aquarium's level affects others through shared clues. |
| Einstein | 15×15 | Large irregular aquariums on a 225-cell grid. Multi-step deduction chains with cascading effects. |
Key strategies at a glance
The first thing to look for is zero-clue rows and columns. If a row's clue is 0, every cell in it is empty. If a column's clue equals the grid size, every cell in it is water. These are free deductions and can eliminate large chunks of the grid immediately.
Next, think about forced fills and empties. If a row needs 3 more water cells and exactly 3 undecided cells remain, all three must be water. If a row has already hit its target count, every remaining cell is air. On harder puzzles, cross-constraint analysis becomes the main technique — one aquarium's water level affects others because they share rows and columns, and those cascading effects are where the real difficulty lives.
Frequently asked questions
What is an Aquarium puzzle?
A grid logic puzzle where you fill irregular regions with water to match row and column clue numbers. Water fills from the bottom and stays level across each region's width.
What are the rules?
The grid is divided into aquarium regions by thick borders. Fill each aquarium with water to some level (or leave it empty). Water is level across the region width and fills from the bottom with no gaps. Numbers outside the grid tell you the filled-cell count for each row and column.
How do I start solving?
Look for rows or columns with a clue of 0 (all empty) or equal to the grid width (all water). Then find rows that need a specific number of cells and have exactly that many undecided. The water-level rule does the rest — filling one cell forces everything below it in the same aquarium to fill too.
What does “water level” mean?
Water level is the height up to which water sits inside an aquarium. Within each column of the aquarium, water fills from the bottom with no gaps — just like a real container. The level is uniform across the full width.
Is this a Nikoli puzzle?
No. Aquarium doesn't appear in Nikoli's catalog. There's no Wikipedia article and no janko.at entry. It was likely created or popularized by the puzzle-aquarium.com website.
Related puzzles
If you enjoy Aquarium, try these:
Binairo
Another binary-state puzzle. Fill cells with 0s and 1s using counting and adjacency rules.
Nonogram
Row and column clues describe groups of filled cells. Similar counting logic, different constraint shape.
Star Battle
Place stars in a grid with row, column, and region constraints. Another puzzle about satisfying count clues.
Light Up (Akari)
Grid deduction with propagation mechanics. Placing a light illuminates entire rows and columns.