Aquarium Fish Stocking Calculator
Search and add fish species to your tank, set each species' count, and instantly see your stocking level, filter recommendation, and any compatibility conflicts. Works for freshwater and marine setups. Nothing uploaded.
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Learn more: fish stocking, bioload, and filter sizing
The 1 inch per gallon rule does not work
The old "1 inch of fish per gallon" rule does not account for bioload, adult size, or temperament. A 1-inch neon tetra and a 1-inch pleco produce vastly different amounts of waste. A single goldfish can overstock a 100-litre tank due to its high bioload. Species-specific bioload ratings give a far more accurate stocking calculation than generic inch-per-gallon formulas.
What is bioload and why does it matter?
Bioload is the amount of waste (ammonia, nitrite, nitrate) produced by fish. It depends on species size, metabolism, and diet. A high bioload means your filter has to work harder to convert waste into less-toxic compounds. Overloading your filter leads to ammonia spikes that can kill fish. This calculator shows your current bioload as a percentage of tank capacity - aim to stay under 80-90%.
Filter sizing for your stocked fish
A general rule is to filter your tank volume at least 10 times per hour. A 100-litre tank needs a filter rated at least 1000 litres per hour. For heavily stocked tanks or high-bioload species like goldfish or cichlids, aim for 15-20x turnover. The calculator recommends a minimum filter size based on your fish mix and total bioload.
Compatibility and temperament
Even if bioload allows more fish, temperament conflicts can make stocking dangerous. Some fish are territorial and will kill tank-mates despite there being "room." The calculator flags known compatibility issues for the species you select - pay attention to these warnings even if the stocking percentage seems low.
FAQ
How many fish can I put in a 100 litre tank?
It depends heavily on the species. Small, low-bioload fish like neon tetras allow roughly 25-30 fish in 100 litres. One goldfish alone can overstock a 100 litre tank due to its high bioload. Use the calculator to get an accurate answer for your specific species mix.
What is bioload in an aquarium?
Bioload is the amount of waste (ammonia, nitrite, nitrate) produced by fish. It depends on species size, metabolism, and diet. A high bioload means your filter has to work harder. Overloading your filter leads to ammonia spikes that can kill fish.
What filter size do I need for my tank?
A general rule is to filter your tank volume at least 10 times per hour. A 100 litre tank needs a filter rated at at least 1000 litres per hour. For heavily stocked tanks or species that produce more waste (like goldfish or cichlids), aim for 15-20x turnover.