AquariumFree tool · Freshwater
Will these fish actually get along?
Pick your tank, add fish, and watch them swim at their adult size. You get plain-English warnings, a stocking estimate, water targets and a shopping list sized to your tank. Every fact links to its source.
Add fish to check
Pick a tank size, then add fish. We'll check every pairing.
1 · Your tank
2 · Your fish
3 · Add fish
Standing at the fish store?
Type the name on the tank label.
We'll check it against your saved tank and tell you yes, careful, or no, plus why.
The first weeks
Cycle your tank before it's full of fish
A new filter has no beneficial bacteria yet. They take weeks to grow. The University of Florida IFAS notes a new biofilter needs six to eight weeks to build up enough bacteria. Log your test results here and we'll tell you where you are.
Test log
| Date | Ammonia | Nitrite | Nitrate |
|---|
Saved on this device only. Need a kit? A liquid test kit reads ammonia and nitrite more reliably than strips. See the test kit guide.
Sized to your build
Your shopping list
Built from your tank and the fish you picked. Links search Amazon so you can compare current options and prices.
As an Amazon Associate, AquariumSetup earns from qualifying purchases. Sizing rules: heater about 5 watts per gallon; filter rated for 4–6× your tank volume per hour; substrate about 1 lb per gallon per inch of depth. These are rules of thumb. Check each product's own ratings.
How it works
What the checks mean
- Red means a hard conflict: the tank is too small for a fish's adult size, two fish need temperatures that don't overlap, or one fish can fit another in its mouth.
- Yellow means it can work with care: a school below its minimum group size, fin-nippers with long-finned fish, a pH or hardness mismatch, or a size gap worth watching.
- Stocking is an estimate based on adult size and waste output (not the old inch-per-gallon rule). Treat it as a guide, not a guarantee. Filtration and maintenance matter.
- Fish are drawn to scale against your tank's length at their published adult size. Stores sell most fish as juveniles.
Where the data comes from
Each species cites the pages its numbers came from. Open any fish to see its sources. Most come from Seriously Fish profiles and FishBase. Catfish also use PlanetCatfish, invasive species the USGS Nonindigenous Aquatic Species database, and cycling science UF/IFAS. Shrimp, snails and the hybrid blood parrot use hobby sources that agree with each other. Values we couldn't source are marked unknown, never guessed.
This tool is a planning aid. Individual fish vary, so watch your tank and ask your local fish store or a vet when in doubt.
Questions
Quick answers
How many fish can I put in my tank?
It depends on each fish's adult size and waste output, not inch-per-gallon. The builder estimates stocking from those against your tank volume. It also checks tank length, group size, water and temperament separately, because a tank can be "under-stocked" and still wrong for a fish.
Why does it say my fish will outgrow my tank?
Many fish are sold at a fraction of their adult size. A common pleco, oscar or bala shark looks tiny in the store. The builder uses published adult sizes and minimum tank sizes and draws every fish full-grown.
Where does the fish data come from?
Mostly Seriously Fish and FishBase, plus PlanetCatfish, USGS and university sources. Every species lists its sources, and anything we couldn't source is marked unknown.
How long does a new tank take to cycle?
UF/IFAS notes that a new biofilter needs about six to eight weeks to build up enough nitrifying bacteria. Fishless cycling with an ammonia source lets you finish before any fish go in. Use the cycle tracker tab to follow along.
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