Rules
Aquarium is a tank puzzle. The board is a square grid. Thick lines are the walls of the tanks. Thin lines are the cells inside a tank. The number left of a row, and above a column, is how many cells in that line are water. A blank slot is not a zero. That line has no fixed count. A printed 0 means the whole line stays empty. You fill a cell with water, or you mark it with a cross when you already know it is empty. Crosses are optional. Water in a tank has one level. Wet rows sit on the bottom. A wet row of that tank is full. Nothing floats above a cell you already know is empty. The puzzle is finished when the water cells are that one set, even if some empty cells are still blank. Play is 6×6, 7×7, 8×8, and 10×10, and each of those is easy, medium, and hard. The daily puzzle is a 6×6 easy grid. People also look this up as an aquarium logic puzzle, or as water fun.
Thermometers also fills from one end to match the outside numbers. There you fill each tube from the bulb. Here you fill each tank from the bottom.
- Thick lines are tanks. The board is a square grid. Thick lines are the walls. Thin lines are the cells inside a tank.
- The number is water cells. The number left of a row, and above a column, is how many cells in that line are water. A blank slot is not a zero. A printed 0 means the line stays empty.
- One level, from the bottom. Wet rows sit on the bottom. A wet row of that tank is full. Nothing floats above a cell you already know is empty.
- Water finishes it. Crosses are optional. The puzzle is finished when the water cells are that one set, even if some empty cells are still blank.
Water sits at row 1 column 1, row 3 column 2, row 4 columns 1–4, row 5 columns 1–5, and row 6 columns 1–3. Everything else stays blank. Row 2 and column 6 are 0, and those empty cells are still blank. The frame is the solved frame. The water is the solved teal. Every number, including both zeros, uses the solved face: saturated teal, white text. No crosses. No yellow ring. A printed answer fills the water and leaves empty cells blank. It does not print crosses.
- Water
- Cross
- Outside number
- Number that matches
- Number that is off
Easy grids in this set print every number. A blank slot shows up on the medium grids, in the wide-tank section and again on the height. This picture has none.
Choose Water or Cross under the board. Tap a cell, or drag across cells, to place that mark. Tap a cell that already has the mark to clear it. A cell with the other mark takes the new one. A drag follows the first cell: it places the mark, or it clears when that cell already has it. One drag is one undo step. With a mouse, right-click places a cross, or clears a cross that is already there. Arrow keys move and stop at the edge. The first arrow, when nothing is selected, selects the top-left cell. Space or Enter places the selected mark, or clears it when the cell already has that mark. W or 1 places water. X, C, E, D, or 2 places a cross. M switches Water and Cross. Backspace, Delete, or 0 clears the cell. There is no cycle through the marks.
While the puzzle is unfinished, the line under the board reads: "Tap a cell, or drag across cells, to place the mark. Tap a mark again to clear it. A blank outside slot is not zero. Press M to switch Water and Cross. With a mouse, right-click places a cross."
Press Hint for one step the rules already force, with a sentence saying why. Hint lights the cells it writes, and the outside numbers of those cells, except a blank slot, which stays empty. Press Check when you want the board checked. A legal unfinished board gets "No mistakes so far. Keep going!" A broken board gets "A tank is uneven or floating, or a row or column count is off. Look for the marked tanks and numbers." Hint on a broken board gets "This board has a mistake, so there is no hint yet." If Hint finds nothing on a legal board, it says "No forced cell from here. A water cell or a cross may be in the wrong place, so try Check or Undo." Undo and Redo step through the moves. Reset clears every water and every cross you placed. The tanks and the numbers stay. When the water cells are the unique set, the board turns teal. The dialog title is "Solved!" The dialog body is "Each tank has one water level, and the outside numbers match." The Mistakes counter counts how many times Check found a broken board. It is not a score.
The ideas, in the order you can use them, are a line of 0, a line whose number matches its length, a line whose number forces the open cells, a one-cell tank, a tank wider than the row, and a cell the column cannot hold. Medium and hard grids then look at every way a row can make its number, and at the water height of one tank. The hardest step tries the other heights of a tank and keeps the height that does not break a clue. The button writes one technique and stops.
While the puzzle is unfinished, an outside number turns teal only when the water count matches and every cell in the line is already marked. That in-progress teal is the muted done face. A printed 0 stays plain while any cell is still blank, so an untouched board does not look finished. When the water set is complete, the board is solved and every number uses the solved face, including a 0 whose empty cells are still blank. That face is the saturated teal with white text, not the muted done wash. A number turns coral when the line already has too much water, or when the cells still open cannot reach the number. A tank turns coral when its water is uneven or floating. The coral is the tank, not a wash along the row. With error highlighting off, none of that coral is drawn.
- Undo
- Redo
- Reset
- Hint
- Check
The outside numbers
The number is how many water cells that line holds. A 0 is empty, and the tanks above those crosses stay empty too. A line whose number matches its length is all water. A line that already has its water, or that still needs water in every open cell, takes the mark the number forces. A one-cell tank is that same arithmetic with its own sentence.
A line of 0 Easy
A printed 0 means that line has no water. The press crosses every open cell on the line. A cross also empties the rest of that tank's row, and every cell of the tank above the cross. On this grid row 2 is 0, so the six cells of row 2 are empty. Five of those tanks continue into row 1, so those five cells of row 1 are empty too. The one-cell tank at row 1 column 1 is not in this press. It is the next section's tank, after the line's number. The 0 on row 2 was plain before the press, because the cells were still blank. After the press that row is fully crossed, so the 0 would be teal once the hint clears. While the hint is up it is amber. Column 6 is also 0. It is not this press. It still has blank cells below row 2, so it stays plain.
A later 0 can be only that one line, when the tanks do not continue above it. On one medium grid the first press is row 1, six crosses, and nothing else. On one hard grid the first press is the same shape, again row 1. Those grids are not drawn. The toast is the whole explanation: "This line is 0, so these cells are empty."
Amber sits on eleven crosses: row 1 columns 2–6, and all six cells of row 2. Each new mark is an ink cross on the amber tile, with a yellow border and a yellow ring. Row 1 column 1 stays an ordinary blank cell. Amber also sits on row 1, row 2, and columns 1–6. The grid is still unfinished, so the toast shows. Hint says "This line is 0, so these cells are empty."
A full line Easy
A number that matches the length of the line fills that line with water. Water fills the rest of that tank's row, and every cell of the tank below the water. On this grid row 6 is 6, so the press is the six cells of row 6 and nothing else. Those tanks do not continue below the bottom of the grid. The cells above them stay blank. Row 6 was plain before the press. It is met after the press, and amber while the hint is up. The columns stay plain, because each of them still has blank cells.
The same sentence can spill into the next row when a tank continues downward. That spill is not drawn. This figure is the clean row. The toast is "This line matches its length, so these cells are water."
The six waters stay ink, each with a yellow ring. There is no amber wash under the water. Amber sits on row 6 and on columns 1–6. The cells above row 6 stay blank. The grid is still unfinished, so the toast shows. Hint says "This line matches its length, so these cells are water."
The number forces the open cells Easy
Once a line is not a 0 and not a full empty line, the number still forces whatever is left. Two shapes, one sentence. If the water already on the line equals the number, the open cells are empty. If the open cells are exactly the water still needed, those cells are water. The press writes those cells, and it closes the level in their tanks.
On this figure row 3's number is 1, and row 3 column 2 is already water, so the other five cells of row 3 are empty. They stay on that one row. The cells of those tanks in row 4 are not written. A cross empties upward, not downward. Row 3 becomes met. It is amber while the hint is up.
The other shape is the next press on this same board, and it is not a second figure. Column 1's number is 4. Three waters are already in that column, and row 4 column 1 is the one cell still open, so it becomes water. That tank also holds row 3 column 1, so this is not the one-cell sentence. The same toast. It does not finish the grid. Ten cells stay unknown. Column 1 becomes met. The press just before the figure writes eight waters: row 3 column 2, row 4 columns 2–4, row 5 columns 1–2, and row 6 columns 1–2. Column 2 still needs four, and the other four are the rest of those wet tank rows. That press is not drawn.
The toast for both shapes is "This line's number forces the open cells."
Amber sits on the five new crosses in row 3: columns 1, 3, 4, 5, and 6. Row 3 column 2 is already water and is not in the write, so it stays ordinary ink, with no hint ring. Amber sits on row 3 and on columns 1, 3, 4, 5, and 6. Column 6 is the printed 0 and is still plain, because rows 4–6 of that column are blank. Row 4 columns 1, 5, and 6 stay unknown. Hint says "This line's number forces the open cells."
A one-cell tank Easy
A tank of one cell is forced by the line it sits on. The arithmetic is the same as the open cells. The sentence is its own, because the only cell the line wrote is that tank. On this grid the 0 has already crossed the rest of row 1. Row 1's number is 1, and row 1 column 1 is the one cell left, so it is water. It is a tank by itself. The press writes that cell and no neighbour.
On the grid from the 0, this is the second press, before the open-cell presses in the previous section. The article still teaches the line first. The toast is "This one-cell tank is forced by the line's number."
A line that writes a one-cell tank and also writes some other cell keeps the open-cell sentence. This press does not.
Ink water at row 1 column 1, with a yellow ring. There is no amber wash under the water. Amber sits on row 1 and column 1. The eleven crosses from the 0 stay ordinary. They are not rewritten. Row 1 is met. Column 1 stays plain: the number is 4, and only one water is in it. The grid is still unfinished. Hint says "This one-cell tank is forced by the line's number."
One tank
One row of a tank can be too wide for the number, so that run is empty. One cell of a tank can be too high for the column, so it stays empty and the rest of that tank row stays empty with it. A row split into two open pieces has only one way to make its number. Those three sentences are in the first group. A 6×6 easy grid does not need them. A medium grid in this article opens on the wide tank.
Wider than the row Medium
If one tank takes more cells in a row than that row's number, the whole run is empty. You do not choose which cells. On this grid row 4's number is 2, and one tank occupies row 4 columns 2, 3, and 4. Three is more than two, so those three cells are empty. Nothing in that tank sits above row 4, so the press does not climb. The cells of the same tank in row 5 stay blank until the next press. That next press is the same sentence: row 5's number is 1, and the tank occupies four cells there, so row 5 columns 1–4 become crosses. That press is not drawn.
Rows 1 and 3 on this grid are blank slots. They are not zeros. This press does not write a cell in those rows, so the blank slots stay empty. The toast is "This tank is wider than the row number, so this run is empty."
A 6×6 easy grid in this set does not say this sentence. A 7×7 easy grid can. The button on this medium board still returns it on an easy puzzle, because the sentence is in the first group.
Amber sits on the three crosses at row 4 columns 2–4, and on row 4 and columns 2, 3, and 4. The blank slots on rows 1 and 3 stay empty. Row 5 columns 1–4 stay ordinary. No number becomes teal. The grid is still unfinished. Hint says "This tank is wider than the row number, so this run is empty."
Too much for the column Medium
Look down one column inside one tank. If the tank has more cells from here to the bottom of that column than the number allows, the upper cell cannot be water. Filling it would fill the cells below it in the tank as well. On this grid column 1's number is 1, and the tank at the top-left has both row 1 column 1 and row 2 column 1 in that column. The upper cell is empty. A cross empties the rest of that tank's row, so row 1 columns 2 and 3 are empty too. They are not a second column argument. The sentence still says "this cell."
Row 1 is a blank slot. It is in the hint's line list because the crosses sit there, and it stays blank. It does not turn amber. Columns 1, 2, and 3 do.
This sentence is in the first group. None of the easy grids in this set say it. The button on this medium board returns it on an easy puzzle. A later press on this board is one cell, row 3 column 1 crossed, with the same toast. That press is not drawn. The toast is "Filling this cell would put more water in the column than the number allows, so it stays empty."
Amber sits on the three crosses in row 1, and on columns 1, 2, and 3. There is no chip on row 1. The earlier crosses on rows 4 and 5 stay ordinary. No numbered clue becomes teal. The grid is still unfinished. Hint says "Filling this cell would put more water in the column than the number allows, so it stays empty."
Two pieces of a row Medium
A row can be split into two open pieces of tank. Every way to make the number uses the same piece, so that piece is water, and the other piece is empty. On this grid row 4's number is 2. One piece is row 4 column 1, one cell. The other is row 4 columns 5 and 6. The only way to make 2 is the wider piece, so row 4 column 1 is empty and row 4 columns 5 and 6 are water. Water fills the cell of that tank below them, so row 5 column 5 is water too. Row 5 column 6 is a different tank and stays blank.
The how-to files "every way a row can make its number" with medium and hard. A row of exactly two open pieces is an easy sentence. A longer row is the next section, and an easy puzzle does not say that one. The toast is the same for both: "Every way to make this row's number agrees on these cells."
A 6×6 easy grid and a 6×6 hard grid in this set do not say the two-piece sentence. A 7×7 easy grid can. This medium board returns it on an easy puzzle.
Amber wash on the new cross at row 4 column 1. Ink water with a yellow ring on row 4 columns 5 and 6, and on row 5 column 5. Amber sits on row 4, row 5, and columns 1, 5, and 6. Row 3 column 1 is already a cross and is not rewritten. Row 4 is met. Row 5 stays plain. The grid is still unfinished. Hint says "Every way to make this row's number agrees on these cells."
The water height
A longer row has more than two open pieces, and every way to make the number agrees on some cells. A short tank then has one water height, so the cells that height fills are written. A hard grid uses the same height sentence on a taller tank. The button does not go on to try the leftover heights one by one.
A longer row Medium
The same agreement runs on a row with three or more open pieces. This row has three: row 2 column 1 alone, row 2 column 2 alone, and row 2 columns 3 and 4 together. The number is 3, and the last two cells of the row are already empty. Both ways to make 3 use row 2 columns 3 and 4, so those two cells are water. The one-cell pieces are not in every way, so they stay blank. The row under them in that tank is already water, so the press writes nothing else.
An easy puzzle returns nothing here. Medium and hard return the hint. The toast is the same sentence as the two-piece row: "Every way to make this row's number agrees on these cells."
Ink water with a yellow ring on row 2 columns 3 and 4. Amber sits on row 2 and on columns 3 and 4. Row 3 columns 4 and 5 are already water and stay ordinary. Row 2 stays plain. The blank on row 3 is not in the line list. The grid is still unfinished. Hint says "Every way to make this row's number agrees on these cells."
One water height Medium
A short tank has only a few possible waterlines. On this grid one height fits. The tank is row 4 columns 1 and 2, row 5 columns 1 and 2, and row 6 columns 1 and 2. The bottom row is already water. The height that fits fills the middle row and leaves the top row empty, so row 5 columns 1 and 2 are water and row 4 columns 1 and 2 are empty. The press writes those four cells. It does not write a neighbour outside the tank.
The toast says "Only one water height fits this tank." On this press that is the grid: one height is left, the bottom two occupied rows of the tank. Other presses in the set still have two heights that only agree on some cells. This sentence does not always mean only one height when the cells it skips are still open. This figure does not skip a cell of the tank.
Row 4 is a blank slot. The crosses sit in that row, so the line list includes it, and the slot stays blank. Column 1 becomes met and is amber while the hint is up. An easy puzzle returns nothing here.
Amber on the two crosses at row 4 columns 1 and 2. Ink water with a yellow ring on row 5 columns 1 and 2. No chip on row 4. Row 6 columns 1 and 2 are already water and are not in the write, so they stay ordinary. Row 4 column 3 is an earlier cross in a different tank and stays ordinary. Column 1 is met and amber while the hint is up. Column 2 and row 5 stay plain, and they are amber too. Twelve cells stay unknown. Hint says "Only one water height fits this tank."
A taller tank Hard
A hard grid can still have a tank with many possible waterlines. The button writes the cells the remaining heights share. On this grid one height fits the tall tank on the right. The press empties row 4 columns 4, 5, and 6, and fills row 5 columns 4 and 6. Row 5 column 5 is a different tank, a two-cell tank of its own, so it stays blank. One cell on the whole grid is still unknown after the press. The grid is not finished, so the toast shows. The next press fills that one cell and finishes. That finish is not drawn.
Rows 4 and 5 and column 6 are blank slots. They are in the line list and they stay blank. Columns 4 and 5 turn amber. Column 4 is met after the press and amber while the hint is up.
The toast is the same sentence as the short tank: "Only one water height fits this tank." On this press one height is left. The tank has six occupied rows. An easy puzzle and a medium puzzle return nothing.
The ladder also has a sentence for trying the other heights of a tank and keeping the one that does not break a clue: "The other water heights of this tank contradict the clues." The how-to calls that the hardest step. On these grids the height sentence had already written the cells, so the button does not say the try. There is no separate picture.
Amber on the three crosses at row 4 columns 4–6. Ink water with a yellow ring on row 5 columns 4 and 6. Amber sits on columns 4 and 5 only. No chip on row 4, row 5, or column 6. Row 5 column 5 stays ordinary and unknown. The water already in the tank, including row 6 column 6, stays ordinary. The toast shows. Hint says "Only one water height fits this tank."
Common mistakes
Check paints a broken rule. Hint will not explain a board that is already broken. The toast is "This board has a mistake, so there is no hint yet." A wrong water or a wrong cross can also sit there with no coral at all. Then Check says "No mistakes so far. Keep going!" and Hint still offers the next real step. The wrong mark stays unless that step writes the cell.
Five pictures, all on the same blank grid as the 0. No amber on the four broken ones. The quiet one may show the opening 0, because the board is legal. Counts that are off paint the outside number only. They do not wash the line. A broken tank paints every cell of the tank.
Row 1 column 2 is water and row 1 column 3 is a cross. The whole tank is coral, including row 2 columns 1 and 2, which are still blank. No outside number is coral. Nothing is amber. Hint on this board says "This board has a mistake, so there is no hint yet."
Row 3 column 1 is water and row 4 column 1 is a cross, in the same tank. Both cells are coral. No outside number is coral. Nothing is amber. Water at row 3 column 1 with row 4 column 1 still blank is not floating. Unknowns below water are not an error. That quiet water is not a second picture. Hint says "This board has a mistake, so there is no hint yet."
Row 2's number is 0. Water at row 2 column 1 is already too many. The row 2 clue is coral. The water cell is not coral. There is no wash along the row. Nothing is amber. Hint says "This board has a mistake, so there is no hint yet."
Column 1's number is 4. Six crosses cannot reach it. The column 1 clue is coral. The six cells are not coral. Nothing is amber. A row that cannot reach its number paints that row's clue the same way. A column with too much water paints that column's clue. Hint says "This board has a mistake, so there is no hint yet."
The four pictures above are what Check paints. A wrong mark Check does not see yet is the other picture. With error highlighting off, the uneven tank, the floating tank, the row clue, and the column clue paint nothing coral.
The cross at row 1 column 1 is water in the solution. One cross does not make row 1 short, and it does not make column 1 short. The tank is one cell, so it is not uneven and it is not floating. No coral. Check says "No mistakes so far. Keep going!" The amber is the opening 0, the same eleven cells as the first figure, and this cross is not among them. The wrong cross stays. A wrong water at row 1 column 2 is also quiet, and that cell is in the opening write, so Hint replaces it with a cross. A quiet wrong mark stays only when the press does not name it.
What to play next
Easy grids follow from the outside numbers. A 0, a full line, the cells the number forces, and a one-cell tank. Start there. The daily puzzle is a 6×6 easy grid, and that size finishes from those sentences. It does not need a tank that is wider than the row, a column that cannot hold the stack, or a two-piece row. A 7×7 easy grid can say the wide tank and the two-piece row. Medium grids add a longer row and the water height of a short tank. The earlier sentences still come first, and a medium grid can still open on a 0, a full line, or a wide tank. Hard grids use the same height sentence on a taller tank. The button on these hard grids does not go on to try the other heights one by one.
- Easy6×6A 0, a full line, the open cells, and a one-cell tank. This is the daily size.Play 6×6 →Today's daily →
- Medium6×6A wide tank, a column the stack cannot hold, two pieces of a row, then a longer row or one water height.Play 6×6 →
12×12 is for print only, and only at medium and hard. There is no 12×12 easy. A printed answer fills the water and leaves empty cells blank. Crosses are not printed. Four 6×6 or 7×7 grids share a sheet. Two 8×8 or 10×10 grids share a sheet. A 12×12 grid has the sheet to itself. The printable page is Aquarium packs.
There is no guide-sized seed to open. The boards above are teaching boards.