This heuristic only screens for obvious overstocking — always research each species individually (temperament, footprint, water chemistry) and confirm with regular water testing before and after adding fish.
Freshwater species stocking chart
Adult size, minimum tank, group needs, and temperature for 55 common freshwater species. Minimums are community-consensus floors — more room is always better.
| Species | Adult size | Min tank | Group | Temp | Notes |
|---|---|---|---|---|---|
| Neon Tetra | 1.2" | 10 gal | 6+ | 70–81°F | sensitive to swings — add only to a cycled, mature tank |
| Cardinal Tetra | 1.75" | 20 gal | 6+ | 73–82°F | prefers soft, warm, slightly acidic water |
| Ember Tetra | 0.8" | 10 gal | 6+ | 73–82°F | nano fish — keep with small, peaceful tankmates |
| Rummynose Tetra | 2" | 20 gal | 6+ | 75–84°F | nose color fades with stress — needs stable, clean water |
| Glowlight Tetra | 1.5" | 10 gal | 6+ | 74–82°F | |
| Black Skirt Tetra | 2.5" | 20 gal | 6+ | 70–80°F | may nip long-finned fish like bettas and guppies |
| Serpae Tetra | 1.75" | 20 gal | 8+ | 72–79°F | nippy — larger groups reduce aggression |
| Congo Tetra | 3" | 30 gal | 6+ | 73–82°F | males grow long fins — avoid fin-nipping tankmates |
| Harlequin Rasbora | 1.8" | 10 gal | 6+ | 72–81°F | |
| Chili Rasbora | 0.7" | 5 gal | 6+ | 70–82°F | nano fish — keep only with tiny, peaceful tankmates |
| Celestial Pearl Danio | 1" | 10 gal | 6+ | 71–78°F | shy — does best in heavily planted tanks |
| Zebra Danio | 2" | 20 gal | 6+ | 65–77°F | very active — prefers a long tank; tolerates cool water |
| White Cloud Mountain Minnow | 1.5" | 10 gal | 6+ | 60–72°F | coldwater — no heater; poor match for tropical tanks |
| Guppy | 2" | 10 gal | 3+ | 72–82°F | breeds constantly — expect fry in mixed-sex groups |
| Endler's Livebearer | 1.4" | 10 gal | 3+ | 72–82°F | hybridizes with guppies |
| Molly | 4" | 20 gal | 3+ | 72–82°F | prefers hard, alkaline water |
| Platy | 2.5" | 10 gal | 3+ | 70–80°F | |
| Swordtail | 4.5" | 20 gal | 3+ | 70–80°F | keep 1 male with 2+ females to spread harassment |
| Bronze Corydoras | 2.5" | 20 gal | 6+ | 72–79°F | needs smooth sand or fine gravel to protect barbels |
| Panda Corydoras | 2" | 20 gal | 6+ | 68–77°F | prefers cooler water than most tropicals |
| Sterbai Corydoras | 2.6" | 20 gal | 6+ | 75–82°F | warm-tolerant cory — a classic discus-tank companion |
| Pygmy Corydoras | 1" | 10 gal | 8+ | 72–79°F | midwater schooler — keep in larger groups |
| Bristlenose Pleco | 5" | 30 gal | solo ok | 65–80°F | needs driftwood to graze |
| Common Pleco | 20" | 75 gal | solo ok | 72–82°F | grows 18-24 in — realistically needs 150+ gal or a pond long-term |
| Clown Pleco | 3.5" | 20 gal | solo ok | 73–82°F | wood-eater — driftwood is required, not optional |
| Betta (Siamese Fighting Fish) | 2.5" | 5 gal | solo ok | 76–82°F | males territorial — one per tank; avoid fin-nippers |
| Dwarf Gourami | 3" | 10 gal | solo ok | 72–82°F | one male per tank; iridovirus common in farmed stock |
| Pearl Gourami | 4.5" | 30 gal | solo ok | 75–82°F | peaceful — keep with calm tankmates |
| Honey Gourami | 2" | 10 gal | solo ok | 74–82°F | one of the most peaceful gouramis — good for small communities |
| Three Spot (Blue) Gourami | 5" | 30 gal | solo ok | 72–82°F | males can bully — watch for aggression |
| Cherry Barb | 2" | 20 gal | 6+ | 73–81°F | peaceful for a barb |
| Tiger Barb | 2.75" | 30 gal | 8+ | 72–78°F | fin-nipper — keep 8+ and avoid slow, long-finned tankmates |
| Rainbow Shark | 6" | 55 gal | solo ok | 72–81°F | territorial — one per tank; provide caves and line-of-sight breaks |
| Angelfish | 6" | 30 gal | solo ok | 75–84°F | needs a tall tank; adults may eat neon-sized fish |
| Discus | 7" | 75 gal | 5+ | 82–86°F | advanced — very warm, soft, pristine water; keep 5+ |
| German Blue Ram | 2.5" | 20 gal | solo ok | 78–85°F | needs warm, stable, mature water — not for new tanks |
| Bolivian Ram | 3.5" | 30 gal | solo ok | 72–79°F | hardier, cooler-water alternative to the German blue ram |
| Apistogramma (Cockatoo Dwarf Cichlid) | 3" | 20 gal | solo ok | 72–84°F | keep one male; needs caves and cover |
| Kribensis | 4" | 20 gal | solo ok | 75–81°F | digs and guards territory fiercely when breeding |
| Kuhli Loach | 4" | 20 gal | 6+ | 73–80°F | burrower — needs sand, hiding places, and a tight lid |
| Clown Loach | 12" | 75 gal | 5+ | 77–86°F | juveniles only at 75 gal — adults need 150+ gal; keep 5+ |
| Hillstream Loach | 2.5" | 20 gal | 3+ | 61–75°F | needs cool, high-flow, oxygen-rich water |
| Cherry Shrimp | 1" | 5 gal | 5+ | 65–78°F | keep only with small, peaceful fish or it becomes food |
| Amano Shrimp | 2" | 10 gal | 3+ | 65–78°F | top algae eater; will not breed in freshwater |
| Ghost Shrimp | 1.5" | 5 gal | 3+ | 65–80°F | often sold as feeders — hardy but short-lived |
| Nerite Snail | 1" | 5 gal | solo ok | 72–78°F | will not breed in freshwater; may leave white eggs on hardscape |
| Mystery Snail | 2" | 5 gal | solo ok | 68–82°F | needs calcium-rich water for shell health |
| Ramshorn Snail | 1" | 5 gal | solo ok | 70–80°F | breeds prolifically — population tracks feeding |
| Fancy Goldfish | 8" | 20 gal | solo ok | 65–75°F | coldwater — 20 gal for the first fish plus 10 per extra; no tropical tankmates |
| Common Goldfish | 12" | 75 gal | solo ok | 55–72°F | pond fish — exceeds 12 in; unsuitable for most home aquaria |
| Otocinclus | 1.8" | 10 gal | 6+ | 72–79°F | needs a cycled, mature tank with biofilm and algae |
| Siamese Algae Eater | 6" | 30 gal | solo ok | 72–79°F | active jumper — often confused with the flying fox |
| Bala Shark | 12" | 120 gal | 4+ | 72–82°F | tankbuster — 12 in active schooler; most homes cannot house it properly |
| Boesemani Rainbowfish | 4.5" | 40 gal | 6+ | 75–82°F | active swimmer — prefers hard, alkaline water and a long tank |
| Dwarf Neon Rainbowfish | 2.75" | 30 gal | 6+ | 73–82°F | active — best in a long, planted tank |
How this calculator works
adjusted-inch-per-gallon with bioload multipliers — a screening heuristic, not a guarantee sum(adultIn × bioload × count) should stay under tank gallons × 0.8 for a filtered, cycled tank It flags species whose minimum tank size exceeds yours, schooling species kept in too-small groups, and combinations whose temperature ranges never overlap.
Keeping the water right matters as much as the head-count: see how often to change aquarium water, our filter & heater combo picks, and hang-on-back filter guide.
Frequently Asked Questions
How many fish can I put in my tank?
A practical screening rule: total adult inches of fish, weighted by how heavy each species’ bioload is, should stay under about 80% of your tank’s gallons — assuming the tank is cycled and filtered. Heavy-waste fish like goldfish and plecos count double or triple.
Is the one-inch-per-gallon rule accurate?
Only as a rough screen for small, slim community fish. It fails badly for heavy-bodied or messy species — a 10-inch common pleco produces far more waste than ten 1-inch tetras. This calculator applies a bioload multiplier per species to correct for that.
Why does my fish combination show a temperature warning?
Each species has a comfortable temperature band. If the bands never overlap — like coldwater white clouds with tropical discus — no single heater setting can keep both healthy, so the combination is flagged.