Aquarium Stocking Calculator

We calculate multiple constraints and take the minimum (the limiting factor):

• Bioload constraint: Mass-based formula (fish_mass ≈ k × length³, bioload ≈ mass^0.75 × metabolism), adjusted for filtration and tank maturity
• Oxygen constraint: Based on surface area and fish activity level - active swimmers need more oxygen
• Swimming space constraint: Horizontal space requirements based on fish length and activity level

The calculator finds which constraint limits you first and shows it as the "limiting factor." This prevents overstocking even in tall tanks with excellent filtration.

Key insight: We separate math (bioload, oxygen) from biology (behavior, compatibility). This gives you a safe biological baseline.

Instead of species lists, we use archetypes that define body shape, waste production, and activity level:

Slim Schooling: Low mass, moderate waste, moderate activity (tetras, rasboras)

Active Schooling: Low mass, higher waste, high activity (danios, rainbowfish, barbs)

Deep-Bodied / Messy: High mass, high waste, low activity (discus, angelfish, large tetras)

Territorial Dwarf: Moderate mass, moderate waste, need territory (dwarf cichlids, gouramis, bettas)

Goldfish: Very high mass, very high waste, moderate activity (all goldfish varieties)

African Cichlids: High mass, high waste, high activity (Mbuna, peacocks)

Bottom Dwellers: Moderate mass, low waste, low activity (corydoras, plecos, loaches)

Reef/Saltwater: Varies significantly by species

Fish grow! A 1-inch fish that will grow to 6 inches needs space for a 6-inch fish. Always plan for adult size to avoid overcrowding as fish mature. This is especially important for species like goldfish, cichlids, and plecos that grow significantly.

Bioload is the amount of waste (ammonia) fish produce. Goldfish produce 2-3x more waste per inch than small tetras. High bioload fish need more filtration and more space per fish. Our calculator adjusts recommendations based on bioload multipliers.

Better filtration can handle more bioload safely. Basic filtration (sponge/HOB) gets 0.85× capacity, standard gets 1.0×, and high-end (canister/sump) gets 1.2×. However, filtration only affects bioload - it doesn't change oxygen limits from surface area or swimming space needs.

This calculator doesn't consider compatibility. Aggressive fish may need more space even if bioload allows more. Territorial fish (cichlids, bettas) may need hiding spots and territories. Always research compatibility before mixing species.

Overstocking leads to:

• Poor water quality (ammonia, nitrite spikes)
• Increased disease risk (stress, poor immune function)
• Aggressive behavior (competition for space)
• Stunted growth (fish don\'t reach full size)
• Shorter lifespans

When in doubt, understock. It\'s easier to add fish later than to deal with a crashed tank.

High Stability: Recommended for long-term success. This is where most stable tanks live. Good margin for error.

Moderate Stability: Acceptable with excellent filtration, frequent water changes, and close monitoring. Less margin for error.

Low Stability: Risky, expert-only territory. Small problems can cascade quickly. Only attempt with exceptional filtration and experience.

These reflect biological stability, not hard limits. We recommend the high stability level for most hobbyists.

New tanks (< 3 months) have less beneficial bacteria and unstable parameters - they can handle 70% of mature capacity. Mature tanks (3-12 months) are fully cycled and stable. Heavily planted mature tanks have better nutrient export and can handle 120% of base capacity thanks to plant buffering.