Four 29-gallon stockings the math approves
Each combo plays to the 29's strength (extra bioload + height) rather than the 20-long's strength (footprint). Click Apply to land in the checker with that combo prefilled.
Angelfish-as-centerpiece community
Apply →One angelfish + eight harlequin rasboras + one bristlenose pleco. The textbook 29-gallon answer. Harlequin rasboras (1.7 in, deeper body) are too big for the angelfish to predate, unlike neons; bristlenose pleco handles algae without outgrowing the tank. Single angel sidesteps the territorial-pair dynamics.
Heavier mid-water school
Apply →Twelve neon tetras + six corydoras + one dwarf gourami. The 29's extra bioload supports a beefier neon school than a 20-long can — twelve is past the comfortable-school threshold and into proper-display range. Dwarf gourami as the centerpiece (note: parameter window is shared, but check your tap GH; gouramis prefer slightly harder water than neons).
Active multi-school
Apply →Eight cherry barbs + ten ember tetras + six corydoras. Three behavioral layers (top-mid, mid, bottom) without a centerpiece. Bioload sits comfortably below 0.7 because all three species are slim-body. Visual interest comes from the layering, not from a single hero fish.
Cool-water hardier mix
Apply →Eight zebra danios + six cherry barbs + six kuhli loaches. Tolerates a wider parameter range — zebra danios accept 64–77°F. Better choice for unheated rooms or houses that run cold; the kuhli loaches are nocturnal so the day-time view is the danio + barb combination.
What still doesn't fit
- Two unbonded angelfish. A bonded breeding pair can sometimes share 29 gallons because they hold the same territory. Two random adults usually means one chases the other to exhaustion. For pairs, 55+ gallons.
- Discus.Still 75+ gallons (group of 3 minimum, ~25 gal each). The 29 doesn't close the gap.
- Common pleco.Adult length still 18+ inches. The 29-gallon is undergrown by the pleco's second year.
- Oscars or large cichlids.Single-fish minimum is 55–75 gallons depending on species; the 29 doesn't fit even an oscar juvenile for more than a few months.
- Multiple male bettas, multiple male dwarf gouramis. Territorial arithmetic doesn't close at this size.
The 20-long vs 29 decision
Same 30 in × 12 in footprint, different heights (12 in vs 21 in), different volumes (16 vs 23 working gallons). Pick by the species, not by “more is better”:
- Pick 20-long when the priority is a bigger school of slim-body schoolers (cories, harlequin rasboras, danios). Floor space drives their behavior; height is unused.
- Pick 29 when the priority is a centerpiece species with vertical body geometry (angelfish, taller-finned gourami) or you want roughly 50% more total bioload for a multi-school community.
Common confusion: beginners assume the 29 is “bigger” in all dimensions because of the higher gallon number. The footprint is identical to a 20-long. If your dream stocking is “a huge school of neons,” you don't actually need a 29 — the 20-long fits an 8-fish school comfortably and the 29's extra headroom goes unused.
When you outgrow 29 gallons
The next meaningful step is 55 or 75 gallons — a 40-breeder is the same footprint as a 29 (just wider front-to-back), so the upgrade is really about getting more floor space. 55s and 75s open angelfish pairs, larger cichlid setups, and bigger schools. The full compatibility checker handles any tank volume you input — set the working gallons and the verdict updates against the same constraint engine this page runs.
Frequently asked
Is a 29-gallon really worth it over a 20-long?
Depends on what you want to keep. The 29 has the same 30 in × 12 in footprint as a 20-long, just 9 inches taller. The extra height unlocks tall-body species (a single angelfish, a centerpiece dwarf gourami pair) that don't fit a 20-long. It also adds about 50% more bioload headroom. But schoolers don't get more room — floor space is identical, so a school of corydoras isn't happier in 29 than in 20-long. Decision: centerpiece species → 29; bigger horizontal school → 20-long stays the right shape.
Can I keep 2 angelfish in a 29-gallon?
Borderline. One adult angelfish needs roughly 30 gallons solo; a bonded breeding pair can sometimes fit 29 because their shared territory replaces individual claims. Two random unbonded angels usually doesn't work — the dominant fish chases the subordinate to exhaustion in tight quarters. The conservative answer is one angelfish in a 29; if pairs are the goal, 55+ gallons gives the retreat space the subordinate needs.
What does the extra 9 inches of height actually do?
Three things. (1) Vertical-body species (angelfish, taller gouramis) get fin clearance — a 21-inch tall tank doesn't compress their geometry. (2) Bioload capacity goes up roughly proportional to volume — the 29 holds about 23 working gallons vs the 20-long's 16, so 40-50% more fish weight fits. (3) Plant options open up — taller stem plants (vallisneria, ludwigia) reach the surface and create vertical interest a 20-long can't host. What it doesn't do: give schoolers more lateral swim space.
Best 29-gallon community for a beginner?
One angelfish + 8 harlequin rasboras + 1 bristlenose pleco is the canonical 29-gallon answer. Angelfish fits the height; harlequin rasboras are big enough (1.7 in adult) that the angel won't predate them like neons; bristlenose pleco handles algae without growing past 5 inches. Parameter window is consistent (warm tropical, soft-acidic to neutral). The math approves it.
Can I keep a school of cardinal/neon tetras with an angelfish?
Risky. Adult angelfish predate small tetras as a documented behavior pattern — the trio of small (under 1.5 in) thin-body fish + cichlid centerpiece is a classic mistake. Harlequin rasboras (1.7 in, deeper body) and pearl gouramis are the angelfish-compatible school-and-centerpiece pairings. If neons are the goal, swap the angelfish for a non-predator centerpiece (dwarf gourami, single bristlenose).
What's the realistic working volume of a 29-gallon tank?
About 23 gallons after substrate, decor, and fill below the rim. The 29 is a slightly more efficient form factor than the 20-long because the substrate footprint is the same but the water column is taller — substrate displaces a smaller percentage of the total volume. Stocking math should still use working volume; the calculator above defaults to 23 for that reason.
Related
- Full compatibility checker →
- Stocking density calculator →
- Angelfish care guide →
- Aquarium volume calculator →
- How many fish in a 20-gallon →
- How many fish in a 10-gallon →
By Jimmy L Wu. Species data uses FishBase for taxonomy, native distribution, and maximum size where the field is populated; husbandry ranges (temperature / pH / GH) and bioload weights are synthesized from established hobby references (Aquarium Co-Op care guides, The Aquarium Wiki, university extension publications) and labeled hobby-practice. Engine logic in lib/aquarium/stocking.ts and lib/aquarium/compatibility.ts. Working volume math assumes ~80% of nominal — the volume calculator handles your specific dimensions if your setup differs. Not veterinary advice — for sick fish or tank emergencies, consult an aquatic veterinarian or a qualified local aquarium professional.