Tools
Tank and equipment calculator
One fish, one tank. Here is what it takes to keep it properly.
Size your setup
Pick the stage your fish is at and whether you are buying for today or for the adult it will become. The numbers follow the same ranges as our care guide: turnover of five to ten times the tank volume per hour, three to five watts per gallon depending on the room, and a weekly water change of a quarter to a third of the tank.
Tank and equipment calculator
Tank size, filter flow, heater watts and water changes for one flowerhorn.
These are minimums that work, not the biggest tank you could buy. Nobody has ever regretted going larger, and a bigger volume is more forgiving of a missed water change.
Why these numbers
- Tank size. An adult flowerhorn needs 75 gallons or more; large males do better in 90 to 125. Juveniles can grow out in something smaller, but only for a while.
- Footprint over height. A 48 by 18 inch tank gives a big fish more room to turn than a taller tank holding the same water.
- Filtration. Flowerhorns eat a lot and mess a lot. Rate the filter for a bigger tank than yours, or run two.
- Heaters. Split the total wattage across two units with guards. A single stuck heater can cook a tank, and a flowerhorn will smash an unguarded one.
- Water changes. Filtration turns ammonia into nitrate. Only water changes take the nitrate out.
Full details are in the tank setup guide and water and temperature guide. Before you add anything else to the tank, read tank mates: the honest answer is almost always one fish per tank.
Questions
Can I keep a flowerhorn in a 55 gallon tank?
A juvenile or a smaller adult female can live in a 55 for a time. A full grown male will be cramped. If 55 gallons is your ceiling, choose your fish accordingly rather than hoping it stays small.
Do I really need two heaters?
Two smaller heaters are safer than one big one, because a single failure does less damage either way. They also heat the tank more evenly.
How often should I change water?
A quarter to a third of the tank, every week, matched for temperature. More if you feed heavily, less never.
Can two flowerhorns share a divided tank?
Sometimes, with a solid divider and enough room on each side, but treat each side as its own tank when you size filtration and water changes. Most keepers find separate tanks less trouble.