Stocking ideas by tank size
Most "stocking idea" articles list twenty fish per tank size and leave compatibility as an exercise for the reader. This page does the opposite: each roster is a complete, compatible community with the parameter overlap verified and the bioload calculated. Click the calculator link under each roster to see the numbers and adjust it.
All rosters assume a planted tank with adequate filtration and weekly 25% water changes. Unplanted tanks or less frequent maintenance should stock lighter.
40 L (10 US gallons)
Small tanks limit options but don't eliminate them. The key is picking species that stay small and don't need a lot of swimming room.
Shrimp colony
- 15-20 cherry shrimp
- 3-5 nerite snails
No fish. Shrimp are the most rewarding thing you can keep in a 40L tank. Cherry shrimp breed readily, graze algae all day, and a mature colony of 50+ individuals is more visually active than most fish communities. Nerites handle the hard algae the shrimp miss. This is the lowest-maintenance option on this page.
Nano schooler
Embers stay under 2 cm and school tightly. Pygmy corydoras are the smallest commonly available cory and occupy the bottom without adding much bioload. Tight fit at 40L; don't add more fish.
75 L (20 US gallons)
The most common starter tank size. Enough room for a real community.
Classic community
The bread-and-butter setup. Neons in the mid-water, corydoras on the bottom, a single honey gourami as the centerpiece. All three species tolerate the same parameters (24-26°C, pH 6.5-7.5, soft to moderate hardness). The honey gourami is peaceful enough to leave the neons alone; a dwarf gourami would also work in this slot but has a higher disease risk from the iridovirus that plagues commercially bred stock.
Betta community
- 1 betta
- 8 ember tetras
- 5 kuhli loaches
- 3 amano shrimp
A betta can work in a community if the tankmates are chosen carefully: nothing with long fins (the betta attacks them), nothing colorful enough to trigger aggression (no male guppies), and nothing that nips fins (no serpae tetras or tiger barbs). Ember tetras are small, dull-colored, and fast enough to avoid trouble. Kuhli loaches are nocturnal bottom-dwellers the betta rarely notices. Amano shrimp are large enough that most bettas leave them alone, unlike cherry shrimp which tend to get eaten. Individual bettas vary; some are peaceful community fish and some are murderers. Have a backup plan.
120 L (30 US gallons)
Room for larger centerpiece fish and bigger schools.
Planted community
Two schooling species at comfortable numbers, a bottom crew that handles cleanup, and a bristlenose for glass algae. Cardinals and harlequins occupy the same mid-water zone without competing because they school separately. Sterbai corydoras tolerate the 26-27°C that cardinals and harlequins prefer, which not all corydoras species do (peppered corydoras, for instance, prefer it cooler).
Gourami centerpiece
Pearl gourami are one of the most underrated centerpiece fish: peaceful, 12 cm, and genuinely attractive with the mosaic scale pattern. Rummynose tetras are the tightest schoolers in the hobby; the group moves as a unit. Otos handle soft algae on leaves and glass. This is a calm, visually cohesive tank.
200 L (55 US gallons)
The sweet spot for medium cichlids and bigger schoolers.
Angelfish community
- 4 angelfish (get 4-6 juveniles, let a pair form, rehome the rest)
- 12 rummynose tetras
- 8 sterbai corydoras
- 1 bristlenose pleco
Angelfish are the classic mid-size cichlid community. The risk: adult angelfish eat anything that fits in their mouth, which includes neon tetras. Rummynose tetras are large enough (4.5 cm) to avoid predation by average-sized angels. Sterbai corydoras tolerate the 26-28°C angelfish need. Don't add cherry shrimp or small rasboras; they'll be eaten.
The pair-forming advice matters. Buy 4-6 juveniles, let them mature and sort out a bonded pair, then rehome the extras. Keeping two pairs in a 200L tank leads to constant territorial war.
Mbuna tank
- 4 yellow labs (1 male, 3 females)
- 4 red zebra (1 male, 3 females)
- 4 maingano (1 male, 3 females)
Malawi mbuna are the opposite philosophy from the planted community: hard alkaline water (pH 7.8-8.5, GH 12-20), heavy rockwork instead of plants, and deliberate overstocking to spread aggression. 12 mbuna in a 200L tank is light by mbuna standards; 16-20 is more typical once the colony is established. All three species stay under 12 cm and are available captive-bred. Spirulina-based pellets, not high-protein food, to avoid Malawi bloat. No plants (mbuna destroy them). No mixing with soft-water community fish.
400 L (100+ US gallons)
Opens up large species and bigger colonies.
Oscar tank
An oscar is a pet, not a community fish. It has personality, recognizes its keeper, rearranges the decor, and eats everything else in the tank. A single oscar in a 400L tank with a bristlenose pleco for glass algae is the right approach. Adding "dither fish" like silver dollars works if the tank is 600L+; in a 400L the oscar and the pleco are plenty of bioload.
Large planted community
- 2 electric blue acara
- 20 cardinal tetras
- 12 sterbai corydoras
- 8 harlequin rasboras
- 2 bristlenose plecos
- 6 amano shrimp
Electric blue acaras are a mild cichlid (related to the green terror but much less aggressive) that coexist with schooling fish when given enough space. A pair as the focal point, two big schools of small fish filling the mid-water, corydoras on the bottom, bristlenoses on the glass, and amanos on the plants. This is the showcase community tank: enough space for every species to behave naturally, enough numbers in each school to see proper schooling behavior, and enough biological diversity to keep the tank stable.
Adjusting these rosters
Every roster above is a starting point. The stocking calculator lets you swap species, change quantities, and see the bioload and compatibility results update live. The calculator links above pre-load each roster so you can modify rather than starting from scratch.
A few things to watch when adjusting:
- If you swap a species, check the parameter overlap. A tank built for 24-26°C soft-water fish can't take a species that needs 20°C or hard water without changing the whole roster.
- The bioload percentages assume weekly 25% water changes. Less frequent changes mean you need to stock lighter.
- Schooling fish have minimum group sizes. Cutting a school from 10 to 4 saves bioload but stresses the fish. Keep schools at or above the recommended minimum.