Tank Size
Tank size picker
- Select your aquarium volume to anchor stocking, parameter, and filter calculations.
- Preset options reflect popular tank sizes, but you can type a custom gallon value anytime.
- Changes update instantly across all cards, so you can compare options before buying equipment.
Select a tank size to begin.
Picking a filter
- Select a model rated for your tank volume, or one size larger if you plan to keep many fish.
- Choosing a product fills in its gallons-per-hour (GPH) flow rate, so water circulation estimates stay accurate.
- Switch to a custom entry if you run multiple filters or adjust the flow rate.
Choose a filter matched to your tank size and use Add Selected when ready.
Choose a filter to estimate how much water flow your tank has per hour.
Tip: press Enter in the GPH field to add quickly.
Current Stock
Responsible Stocking Checklist
- Verify your nitrogen cycle is complete—showing zero ammonia and zero nitrite—before adding any fish.
- Match species by temperature, pH, and hardness tolerances, focusing on the overlapping range where all can thrive.
- Add new fish gradually over several weeks, giving your beneficial bacteria time to adjust.
- Consider adding extra biological filter media to handle increased waste as you add more fish.
- Keep a quick log of maintenance, feedings, and behavior changes so you can catch problems early.
Your selected fish and inverts appear here. No stock yet. Add species to begin.
Environmental Recommendations
Environmental Card Guide
- These ranges show the overlapping temperature, pH, hardness, and flow preferences of your selected fish.
- Alerts appear when your planned fish fall outside compatible ranges, so you can adjust your selection or equipment.
- Use these guidelines as a starting point, and always verify with your own water tests before adding fish.
Based on your selected stock.
Plan Your Stock
Plan Your Aquarium with Confidence
The Stocking Advisor helps you build a calm, healthy tank. It uses real-world stocking data and hobby feedback to show you—at a glance—how your choices affect bioload, filtration needs, and species mix. No spreadsheets. No guesswork.
How to use the Stocking Advisor
- Choose your tank size. Pick a preset volume or enter a custom gallon value so every card uses the right baseline.
- Add your filter. Select a model or type in a custom gallons-per-hour value so the tool can estimate water circulation.
- Enter current and planned fish. Search for species, set quantities, and keep the list updated as your ideas change.
- Review the cards. Check the bioload meter, compatibility banner, and Environmental Recommendations for temperature, pH, and hardness overlap.
- Tune your plan. Adjust fish choices, water chemistry targets, or equipment until alerts clear and the ranges fall into the shared safe zone.
The Science Behind the Recommendations
Bioload, not “inches per gallon”
The Stocking Advisor calculates aquarium bioload—how much waste your fish produce—using conservative stocking rules and activity multipliers. Fast swimmers (like danios) add more load than slow cruisers (like gouramis). This tool assumes you’re starting a fresh setup, so your filter sets the biological capacity at first. Once you add dense, fast-growing plants, revisit your stocking plan because those plants help process waste too.
Water chemistry guidelines
Each species carries preferred ranges for temperature, pH, and hardness. If your plan mixes fish with different water needs, the Environmental card highlights it so you can adjust fish selection, tune water chemistry, or change heat and flow equipment.
Compatibility and behavior
The Advisor warns about known problem pairs—fin nippers with long fins, shrimp-unsafe hunters with inverts, or aggressive fish with peaceful schooling species—so you can fix issues before they’re in the water.
When your plan looks good, head to the Gear Guide to match filters, heaters, and lights, or brush up on water testing in the Cycling Coach.
Want to share your success? You can submit your tank to be featured alongside other community tanks, or see featured tanks from the community.
Aquarium Bioload & The Nitrogen Cycle
Every fish you preview in the Stocking Advisor contributes to the system's bioload, which is the sum of waste, respiration, and uneaten food the filters must process. Beneficial bacteria living on hard surfaces convert toxic ammonia into nitrite and then into less harmful nitrate—but nitrate still needs regular water changes to stay low. Keeping the nitrogen cycle stable means adding fish slowly, rinsing filter media in dechlorinated water, and tracking test results so you can dial in water changes before nutrients creep beyond safe ranges.
Stocking Advisor FAQ
What data powers the compatibility alerts?
The tool generates compatibility alerts using species-specific behavior profiles, water chemistry needs, adult size, aggression levels, and territorial requirements.
The system also uses a conservative model built from verified husbandry references and hobbyist outcomes to avoid risky combinations like pairing aggressive cichlids with peaceful tetras or long-fin fish with fast nippers.
How is aquarium bioload calculated?
Bioload is estimated from each species' adult size, activity level, feeding response, and habitat preference, and the system intentionally assumes higher waste output so active schooling fish count heavier than slow bottom-dwellers of similar size.
What if my fish or invertebrate isn't listed?
If a species you want isn't listed, use the closest match with similar size and behavior for general planning, and note any unique needs. You can request new species additions through our Contact & Feedback page — we prioritize commonly requested fish.
What is the aquarium nitrogen cycle?
The nitrogen cycle is the multi-week process where beneficial bacteria convert toxic ammonia into nitrite, then into less harmful nitrate — but nitrate still needs regular water changes to stay safe.
How often should I update my stocking plan?
Update your plan whenever tank size, filtration, or fish change, when you notice unusual behavior or water test results, or when plant growth, tank maturity, or filter performance shifts bioload.
Can I use this tool for saltwater tanks?
Not yet. The Stocking Advisor currently supports freshwater community, semi-aggressive, planted, and low-tech tanks, with saltwater support planned for a future expansion.
How accurate is the bioload calculation?
Bioload estimates are intentionally conservative to keep beginners safe. They’re most accurate with common community fish. Results will vary based on your tank’s maturity, plant growth, and filter performance.
What's the difference between bioload and the inch-per-gallon rule?
The inch-per-gallon rule counts only fish length, while bioload modeling accounts for activity, body mass, oxygen demand, waste production, and behavior, making it safer and more realistic for modern tanks.
Can I override compatibility warnings?
You can override compatibility warnings if you understand the risks, but we recommend beginners follow them to avoid stress and fish loss.