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
- Powered filters (hang-on-back, canister, internal) are checked by their rated flow in gallons per hour (GPH) and the turnover it gives your tank.
- Sponge filters are checked by the manufacturer’s tank-size rating, not by flow. Their water flow is not estimated.
- Powerheads move water but hold no filter media, so they count as circulation only.
- Not in the list? Add a custom filter: enter GPH for a powered filter, or the rated tank size in gallons for a sponge.
Choose a filter matched to your tank size and use Add Selected when ready.
Add your filter to check it for your stock. Powered filters are checked by their flow (GPH); sponge filters by their manufacturer tank rating. Powerheads count as circulation only.
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 add a custom filter: enter gallons per hour for a powered filter, or the manufacturer’s rated tank size for a sponge filter.
- 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.
- Use the result as a planning screen. Adjust fish choices, equipment, or water targets when alerts appear, then verify adult size, behavior, tank footprint, and your own water tests before buying or adding livestock.
The Science Behind the Recommendations
Bioload, not “inches per gallon”
The Stocking Advisor estimates aquarium bioload—how much waste your livestock add for the tank to process—from each species’ adult size, body shape, and waste output, so a few large, deep-bodied fish can load a tank far more than a school of small ones. The percentage is a planning estimate, not a measured capacity. The percentage assumes a working, established (cycled) filter; the filter is checked separately and does not change the percentage. A new filter needs several weeks to grow the bacteria that process waste, so stock gradually and revisit your plan as the tank matures.
Filtration does half the work on bioload, but safe stocking still depends on tank maturity, water quality, and species compatibility.
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.
Important limits before you stock
The Stocking Advisor is a conservative planning tool, not a guarantee that a fish community will thrive. A result can help you spot likely bioload, compatibility, and water-parameter problems early, but it cannot see your aquarium’s true biological maturity, maintenance routine, plant growth, oxygen level, individual fish behavior, or the condition of livestock at purchase.
Before adding fish or invertebrates, confirm each species’ adult size, minimum tank footprint, social-group needs, temperament, and long-term care requirements. Test your actual water, make sure ammonia and nitrite are both 0 ppm, introduce livestock gradually, and pause if fish show stress, illness, aggression, or breathing difficulty.
Do not use a cleared result to justify overcrowding, mixing fish with incompatible welfare needs, or adding livestock to an uncycled aquarium.
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 and body shape, so a deep-bodied 3-inch fish counts several times more than a slim 1-inch fish. Shrimp and snails count less than fish of the same size, grazers that live on algae and biofilm count a little less, and heavy waste producers such as plecos count more. It is an advisory estimate for comparing stocking plans, not a measured carrying capacity.
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, 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. Treat the result as a cautious starting point and verify it with regular ammonia, nitrite, nitrate, and behavior checks after any stocking change.
What's the difference between bioload and the inch-per-gallon rule?
The inch-per-gallon rule counts only fish length, so a 6-inch fish counts the same as six 1-inch fish. The Stocking Advisor’s bioload estimate also accounts for body mass, through adult size and body shape, and for waste output, so larger and deeper-bodied fish count much more than their length alone suggests.
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.