1
Enter your tank volume
Type in your aquarium size in gallons. Use true water volume if you already know it from a volume calculation.
Fish Tank Stocking Calculator
A fish tank stocking calculator estimates how heavily your aquarium is stocked by comparing tank size, filtration, and each fish's adult size and bioload. It helps you avoid overstocking, aggression, and water quality problems before you add new livestock.
Tank Setup
Enter your display tank size, then choose the filtration style that most closely matches your system.
Use actual system gallons if you already know your true water volume.
Filtration type
Fish List
Add the fish you want to keep. The calculator scores each fish at adult size, not juvenile size.
Stocking Results
Stocking percentage compares your fish list to the estimated safe capacity for this tank and filtration setup.
Comfortable
0%
You still have room to grow, assuming maintenance and water quality stay consistent.
Green: under 70%
Yellow: 70-90%
Red: above 90%
What this means
You have capacity for about 18 more small 2-3 inch peaceful fish equivalents.
This estimate assumes regular maintenance, stable salinity, and good oxygen exchange.
0
Fish count
Total individual fish in your list
0
Bioload points
Adult size adjusted for bioload and temperament
43.2
Safe capacity
Based on 75 gallons and sump filtration
43.2
Remaining capacity
Negative numbers mean the list is beyond the recommended range
Selected Fish Breakdown
Review each species at adult size before you buy livestock.
Add fish above to see a species-by-species stocking breakdown.
Common Saltwater Fish Reference
This built-in species database covers 36 common reef and saltwater fish used by the calculator.
| Species | Adult size | Bioload | Min tank | Temperament | Reef-safe |
|---|---|---|---|---|---|
Azure Damselfish | 3" | medium | 30g | semi-aggressive | Yes |
Banggai Cardinalfish | 3" | low | 30g | peaceful | Yes |
Bicolor Blenny Bicolor blennies are reef-safe with caution because some individuals may nip fleshy corals or clam mantles. | 4" | medium | 30g | semi-aggressive | With caution |
Blue Green Chromis | 3.5" | medium | 30g | peaceful | Yes |
Blue Tang Blue tangs need long swimming lanes and stable water quality as they mature. | 10" | high | 125g | semi-aggressive | Yes |
Carpenter's Flasher Wrasse | 3.5" | low | 30g | peaceful | Yes |
Chalk Bass | 3" | low | 30g | peaceful | Yes |
Copperband Butterflyfish Copperband butterflyfish can be delicate feeders and may pick at tube worms or some corals. | 8" | medium | 75g | peaceful | With caution |
Coral Beauty Angelfish | 4" | medium | 55g | semi-aggressive | With caution |
Diamond Watchman Goby | 6" | medium | 40g | peaceful | Yes |
Engineer Goby Engineer gobies grow very large and can undermine unsecured rockwork as they dig. | 12" | high | 125g | peaceful | Yes |
Firefish Goby | 3" | low | 20g | peaceful | Yes |
Flame Angelfish | 4" | medium | 70g | semi-aggressive | With caution |
Flame Hawkfish Hawkfish are reef-safe with caution because they may prey on very small shrimp and ornamental crustaceans. | 4" | medium | 30g | semi-aggressive | With caution |
Foxface Rabbitfish Foxfaces have venomous spines and need ample swimming room as adults. | 9" | high | 125g | peaceful | With caution |
Kole Tang | 7" | medium | 70g | semi-aggressive | Yes |
Lawnmower Blenny | 5.5" | medium | 40g | peaceful | Yes |
Longnose Hawkfish Longnose hawkfish are reef-safe with caution because they may eat small shrimp or crabs. | 5" | medium | 30g | semi-aggressive | With caution |
Lyretail Anthias Lyretail anthias do best with frequent feeding and steady, low-nutrient filtration. | 5" | medium | 70g | peaceful | Yes |
Mandarin Dragonet Mandarin dragonets usually need an established tank with a large copepod population before they thrive. | 3" | low | 50g | peaceful | Yes |
Maroon Clownfish | 6" | high | 55g | aggressive | Yes |
Melanurus Wrasse | 5" | medium | 55g | semi-aggressive | Yes |
Midas Blenny | 6" | medium | 30g | peaceful | Yes |
Neon Goby | 2" | low | 10g | peaceful | Yes |
Ocellaris Clownfish | 3.5" | medium | 20g | semi-aggressive | Yes |
Orchid Dottyback | 3" | medium | 30g | semi-aggressive | Yes |
Pajama Cardinalfish | 3.5" | low | 30g | peaceful | Yes |
Percula Clownfish | 3" | medium | 20g | semi-aggressive | Yes |
Purple Firefish | 3.5" | low | 20g | peaceful | Yes |
Royal Gramma | 3" | low | 30g | peaceful | Yes |
Six Line Wrasse | 3.5" | medium | 30g | aggressive | Yes |
Tailspot Blenny | 2.5" | low | 20g | peaceful | Yes |
Tomini Tang | 6" | medium | 70g | semi-aggressive | Yes |
Yellow Coris Wrasse | 5" | medium | 50g | peaceful | Yes |
Yellow Tang | 8" | high | 75g | semi-aggressive | Yes |
Yellow Watchman Goby | 4" | low | 30g | peaceful | Yes |
Want to log the fish you choose over time? Track livestock and maintenance in the My Reef Log app.
How To Use This Stocking Calculator
2
Choose your filtration style
Pick HOB, canister, or sump to adjust the calculator for gas exchange and filtration headroom.
3
Add fish and quantities
Select each saltwater fish species and quantity. The tool uses adult size, bioload, and temperament for the estimate.
4
Review stocking percentage and warnings
Use the color-coded stocking level plus tank size and compatibility warnings to see whether the plan is realistic.
Frequently Asked Questions
How many fish can I keep in my saltwater tank?
The right number depends on adult fish size, bioload, temperament, filtration, and aquascape rather than a simple fish-per-gallon rule. A 75 gallon tank can safely hold a very different fish load depending on whether it houses gobies and cardinals or tangs and rabbitfish.
Is the one inch per gallon rule accurate for reef tanks?
No. Saltwater fish produce very different bioloads, and active species like tangs need far more swimming space than their body length suggests. A stocking calculator based on adult size, filtration, and compatibility is more useful than the one inch per gallon rule.
Does better filtration let me keep more fish?
Better filtration increases safe capacity to a point, especially if you run a sump with strong gas exchange and maintain the tank consistently. It does not remove minimum tank size or compatibility limits for species that need swimming room or peaceful tankmates.
What stocking percentage is considered safe?
As a general rule, under 70 percent is comfortable, 70 to 90 percent is a caution zone, and anything above 90 percent should be treated as overstocked. Staying below the red zone gives you more room for growth, feeding mistakes, and nutrient swings.
What does reef-safe with caution mean?
Reef-safe with caution means a fish often works in reef aquariums but may still nip corals, clams, shrimp, or other invertebrates depending on the individual. These fish should be added only after you understand the tradeoff for your coral and cleanup crew plan.
Related Reef Tools
Aquarium Volume Calculator
Figure out your true water volume before you estimate stocking.
Water Parameter Calculator
Check whether nitrate, phosphate, and salinity match your fish load.
Dosing Calculator
Calculate exact supplement adjustments after stocking changes.
Salt Mix Calculator
Plan saltwater for water changes when your bioload increases.
Plan Stocking, Then Track It
After you choose the right fish load, My Reef Log helps you keep records of livestock, maintenance, and water tests in one place.