Fish Tank: the gameplay guide

The short version

• Feed a little and often. Food nobody eats rots on the sand and dirties the water.
• Clean before the water turns murky. Press Clean, then the parts of the tank that need it, or hold Clean for the whole tank.
• Happy fish earn shells. Spend them on more fish, plants and a bigger tank; levels unlock the rest.
• A happy, fed, healthy pair lays eggs. A breeding box stops hungry fish eating them.
• Two rare parents can hatch a one-of-a-kind fish. There are twelve to find.
• Time away is gentle. Closed or untouched for 12 hours, the tank runs at half speed for up to three days, and nothing dies of it.

Simulation or Casual

The first setting decides the stakes. Both modes play the same in every other way: fish get hungry, the water gets dirty, happiness rises and falls and shells are earned at the same rate. You can switch at any time.

Keys and dials

A hold is any press of more than about half a second (600 ms). Everything happens when you let go.

On the shop, fish and settings pages, Back is bottom left and the key beside it goes round shop, Your fish, settings. The More page holds Settings, Snapshot, Lights, the Screensaver, Status, the Shop and Your fish, as many as your deck has room for. On a Stream Deck Mini, hold the tank for the shop and hold Status (on the More page) for Your fish.

Stream Deck + dials:

• Feed: turn to aim, push or touch to feed there.
• Clean: turn to pick a column of the tank, push or touch to clean it. No cleaning mode needed.
• Lights: turn, push or touch to cycle auto, on and off.
• Go: turn to pick Tank, Shop, Fish or Back, push to go; touch reads the next news.
• Tank dial (for your own pages): a live view; push or touch opens the tank, a touch-hold opens the shop.

Feeding

• A fish eats while it is less than 93% full. The hungriest fish gets to the food first.
• Each pellet fills a fish by the food's value: flakes 30%, sinking pellets 40%, frozen brine shrimp 52%. Fry get half as much again from each.
• Food nobody eats sinks, and two minutes after it lands it rots into dirt where it lies. Pellets make 15% less mess than flakes, frozen food 30% less.
• A fish is hungry below 25% full and starving at empty. Fish get hungry 40% slower at night, and fry 20% faster.
• A starving fish loses health slowly: about three days from full health to none, with "sick" and then "dying" warnings long before.

Clean water

• The tank is ten strips side to side, and each gets dirty on its own. The two end strips dirty 40% faster, and a dead fish fouls the strip it lies in.
• More fish dirty the water faster, but it is measured against the size of the tank: a big tank full of fish clouds no faster than a small tank full.
• Plants and some decor keep the water clearer, up to 60% slower. However well planted, it still needs cleaning. A brighter light grows more algae.
• Above 60% dirty: "The tank needs cleaning". Above 85%: "The water is filthy". Above 80% it starts to cost health.
• Cleaning an area resets it to clean and scoops out any dead fish lying there. A dead fish can only be removed by cleaning.

Happiness and health

Each fish's happiness drifts towards a target made of:

• Being fed: the biggest part, full marks from 60% full.
• Clean water.
• Plants and decor: up to +15% in all. Better food adds a little: pellets +2%, frozen +5%.
• Company: neon tetras want at least three of their kind, firefish two; either is unhappy alone. Two adult bettas upset each other.
• Room: each fish or egg over the tank's size costs happiness.
• A dead fish in the tank, or poor health, costs happiness too.

Fish above 50% happy earn shells; above 60% they earn XP; above 75% (and fed and healthy) a pair can breed. Health comes back fast: from nothing to full in two hours, as long as a fish is fed (over 30%), the water is under 70% dirty and nothing else is harming it.

Day, night and the lights

• By default the tank's day runs 08:00 to 22:00 on your computer's clock; Day starts and Day ends change it.
• The Lights setting can follow the clock, stay on or stay off.
• At night the tank is dark, the fish drift slowly near the bottom with their eyes closed, and they get hungry 40% slower.

Time away

• When Stream Deck is closed, the first ten minutes play in full; after that the tank runs at half speed, for at most three days.
• When Stream Deck is running but nobody has pressed a key for 12 hours, the same rules apply until your next press. The fish keep swimming on screen.
• Away, nothing dies: health cannot drop below 25% (or below where it already was). Fish do not eat eggs and the lionfish does not hunt.
• Eggs are laid and hatch, shells and XP are earned, shells turn up in the sand, and the shop restocks, all while you are away.

Shells and XP

• You start with 20 shells.
• Happy adults earn shells (over 50% happy), more the happier they are, more for better species and rarer fish. The first four fish earn in full; beyond that each earns a little less (eight fish about 71% each, sixteen about half), so a crowded tank earns more in total but not in proportion.
• Shells in the sand: while any fish is alive, about one turns up every two hours, up to three at a time, each lasting eight hours. Press the tank key it lies under. They are worth about 7 at level 1, rising to about 32 at level 11.
• XP comes from happy fish (up to 4 an hour for the whole tank, which eight happy fish reach), 5 for every egg that hatches, cleaning a dirty area (up to 2 for the whole tank), and rehoming (3 for an adult).
• The Shells and XP settings multiply them 1x, 2x, 5x or 10x. Shells covers what fish earn and what you find in the sand.
• Rehoming pays half the shop price (half again for a fry), scaled by rarity. It is never multiplied, so buying and rehoming cannot be farmed.

Levels and unlocks

XP needed for each level: 40, 120, 260, 480, 800, 1,250, 1,850, 2,600, 3,600 and 5,000 (level 11 is the top). Prices are in shells. F is freshwater only, S saltwater only.

Only the next tank, light and food up are on the shelf at a time. Foods and backgrounds are bought once; after that you can switch between the ones you own for free.

The fish

Each kind comes in several named colour varieties. A tank holds as many fish as its size, counting unhatched eggs; the clean-up crew do not count.

Eggs and fry

• A pair breeds when both are grown, over 75% happy, over half full and over 80% health. Then each hour there is a small chance the female lays, depending on the kind: guppies most often, golden guppies and plecos least.
• A clutch never overfills the tank: it is cut down to the room left. After laying, a female rests before she can lay again (a day and a half for a guppy, up to five days for a pleco or golden guppy).
• Eggs hatch in about 20 to 36 hours. "Eggs hatching soon" shows in the last six. Each egg that hatches gives 5 XP.
• Hungry fish eat eggs. Adults below 35% full go after them, and the more hungry fish, the faster. A breeding box (level 2, 35 shells) keeps every egg safe. Nothing eats eggs while you are away.
• Fry start at half size, get hungry faster but get more from each pellet, and earn nothing until they grow up (two to six days). Rehoming a fry pays half an adult's worth.
• The Roster key on Your fish says what is holding eggs back: no grown pair, fry still growing, no room, or a pair that needs to be happier.

Rarity and one-offs

• Fish come as Common, Uncommon, Rare, Legendary or Unique. Uncommon fish shimmer more; Rare and Legendary ones have colours no shop variety has, and twinkle in the tank.
• The shop restocks once a game day, and the fish on the shelf is exactly the one you get. Odds per fish: Uncommon 6%, Rare 1.2%, Legendary 0.2%. The news says when something good is in.
• Breeding is better: Uncommon 15%, Rare 4.5%, Legendary 1.2%, and the rarer the parents, the better the odds. A pair of Rares has four times the luck of a common pair. Food, decor and happiness do not change the odds; happiness only decides whether a pair breeds.
• Babies take their colours from either parent, with the odd small change.

One-offs. When both parents are Rare or better, each egg has an 8% chance of hatching a one-of-a-kind fish with its own name, colours and markings. There is one for every kind of fish, and each can only ever hatch once in a tank. A pair goes for its own kind's one-off first, then others in its family. Your record counts how many of the twelve you have had.

Clownfish are the only saltwater fish that breed, so the reef one-offs all come from a Rare-or-better clownfish pair, Ribbon first.

The clean-up crew

Shrimp and snails graze algae off the glass, and shrimp also pick up leftover food before it rots. They do not count towards the tank's size: a tank has room for 2, 3, 5 or 8 of them, by size.

Crew never die of hunger, but a spotless tank leaves them little to eat ("The crew have nothing to eat"), and water dirtier than 85% harms them.

Plants, decor and upgrades

• Every plant and ornament adds a little happiness (up to +15% in all). Plastic and live plants, moss balls, lava rock, live rock and the wavemaker also keep the water clearer.
• Live plants need the planted light; coral and anemones need the reef light (the reef light counts as planted too).
• Each item has a limit: six plants of each kind, a few rocks, one chest, castle or breeding box.
• A bigger tank holds more fish (4, 8, 14 or 22) and more crew. Upgrading keeps everything in it.

Changing the water

• The Marine setup (level 4, 150 shells) turns the tank to saltwater; the Fresh setup (60) turns it back.
• It cannot be done while eggs are waiting to hatch, or while any fish or crew could not live in the new water: rehome those first (you get the usual refund).
• Decor that does not suit the new water is packed away, not lost, and comes back if you change back. The tank, light, food and background stay.
• An empty saltwater tank with too few shells for a new pair is given clownfish, the way a freshwater one is given guppies.

Illness

Off unless you turn it on. With it on, fish can catch white spot, in either mode.

• Dirty water (over 60%) gives it a small chance each hour of striking the weakest fish; a fish from the shop has a 3% chance of arriving with it; an ill fish can pass it to the nearest well one.
• It wears health down slowly: about eight days to kill a fish that is otherwise looked after, and never in Casual.
• It clears by itself after a day of clean water (under 65% dirty) and a fed fish. The White spot cure (55 shells, only in the shop while Illness is on) clears every ill fish in six hours and stops it spreading meanwhile.
• With a breeding box, the next fish to fall ill moves into it by itself and cannot pass it on.

Warnings and news

The Tank key's rim shows the worst thing going on: green when all is well, amber for a warning, red and blinking when something is wrong. The same shows on the Status key, the Go dial and the fish cards.

News (deaths, hatchings, eggs laid, levels, grown fry, eggs eaten, good fish in the shop, illness) waits on the Status key; press it to read the next. A death while you are watching also flashes Stream Deck's warning on the Tank keys.

Settings

On the deck (hold Back on the tank page, then Settings) or in any Fish Tank key's settings in Stream Deck. Press a setting to step it on, hold it to step back.

• Mode: Simulation or Casual.
• Illness: off or on.
• Shells and XP: 1x, 2x, 5x or 10x.
• Lights: follow the clock, always on, always off. Day starts 05:00 to 11:00 and Day ends 16:00 to 23:00.
• Across decks: one tank across several Stream Decks, left to right or right to left.
• Smoothness: 2 to 15 frames a second on the tank page (8 by default). Lower it if the computer feels busy.
• Your record, How to play, and Start over (press twice within 4 seconds; the old tank is kept as fishtank-previous.json).

The tank saves itself every 30 seconds to %APPDATA%\DeckPets\fishtank.json, with a backup beside it.

Tips

• Buy a breeding box early. At 35 shells it is the cheapest way to keep every clutch, and it doubles as a sick bay.
• Feed where the fish are. Press the tank where they swim rather than Feed, and less food goes to waste.
• Clean little and often. Cleaning a dirty area also earns XP, and happy fish in clean water earn more.
• Four fish earn in full. Past that, each fish earns a little less; a bigger tank is about room to breed, not only income.
• Keep your best fish. Rare parents breed rarer babies, and two Rares are the only way to a one-off.
• Schools need numbers. Buy neon tetras in threes and firefish in pairs.
• Only one betta, unless you want an unhappy tank.
• Crew for a busy tank. Shrimp catch the food you over-pour; snails keep the glass down between cleans.