Aquarium Stocking Calculator

Planning a new aquarium is exciting — but adding too many fish, or mixing incompatible species, leads to poor water quality, stressed fish, and costly losses. This aquarium stocking calculator gives you a professional-grade analysis before you spend a dollar at the fish store.

Step 1: Configure Your Tank

Enter your tank size in gallons (or switch to liters with the toggle). Select your tank shape — bowfront, hexagonal, and cylinder tanks have less surface area than rectangular tanks of the same volume, which limits gas exchange and effective stocking capacity. Choose your filtration type: a canister filter can support 20% more bioload than a basic HOB, while a sump is the gold standard for saltwater reef tanks. If you have live plants, enable the Planted Tank toggle — aquatic plants absorb nitrogen and reduce bioload by roughly 12%.

Step 2: Enter Water Chemistry

Optionally enter your target temperature, pH, and hardness. The calculator uses these values to generate precise warnings when a species you add falls outside the safe range. For example, a Discus cichlid needs 82–88°F and pH 5.5–7.0 — conditions incompatible with White Cloud Minnows, which prefer 60–72°F. Entering chemistry prevents these mismatches before you buy fish.

Step 3: Search and Add Species

Type any common name, scientific name, or category into the search box. Results appear instantly — click Add to place the species in your tank. The calculator defaults to the minimum school size for schooling fish (e.g., 6 Neon Tetras, 4 Corydoras) because keeping schooling fish in groups below their minimum causes chronic stress and reduces their lifespan. You can adjust quantities up or down after adding.

Step 4: Review Stocking Analysis

The stocking level bar shows your bioload as a percentage of effective tank capacity. Under 75% is the target for most hobbyists — your biological filter has headroom to handle spikes. At 75–100%, you need strong filtration and consistent weekly water changes. Over 100% means your fish are at risk: ammonia and nitrite spikes will cause disease and death. The effective capacity shown accounts for filtration quality, tank shape, and planted status.

Step 5: Check Compatibility Warnings

The calculator checks every pair of species in your tank for compatibility conflicts, using each species' temperament tags and incompatibility list. It also checks whether your entire stock has overlapping temperature and pH ranges. Common issues flagged: mixing freshwater and saltwater fish (absolute prohibition), placing Tiger Barbs with long-finned species (fin nipping), adding schooling fish below their minimum group size, and mixing aggressive cichlids with peaceful community fish.

Step 6: Save or Share Your Plan

Your entire tank configuration — species list, quantities, tank size, water chemistry, and settings — can be encoded into the URL. Click Save to URL to update your browser's address bar, or Share Link to copy a shareable URL to your clipboard. Send it to other hobbyists or your local fish store so they can see exactly what you are planning.

Understanding the Species Database

The calculator includes 110+ species across freshwater and saltwater categories. Freshwater species include community fish (tetras, rasboras, danios, livebearers), catfish, loaches, invertebrates, semi-aggressive species (gouramis, rams, angelfish), and large/aggressive species (Oscars, Jack Dempseys, Arowanas). Saltwater species include reef-safe community fish (clownfish, gobies, cardinals), semi-aggressive reef residents (tangs, dwarf angelfish), and aggressive predators (lions, triggers, groupers). Each species entry contains temperature range, pH range, maximum adult size, minimum school size, temperament, and compatibility tags that drive the warning logic.