Keeping community fish in a home aquarium requires understanding the water chemistry preferences, social behaviour, and feeding habits of each species present. Grouping species with incompatible requirements — whether in terms of temperature, water hardness, or aggression level — typically results in chronic stress and elevated susceptibility to disease.
The species profiled here are among those most commonly available in Polish aquarium shops and represent a range of size, behaviour, and habitat preference. Parameter values are drawn from published species databases and reflect conditions in which these fish have demonstrated stable long-term health.
Schooling Fish
Paracheirodon innesi — Neon Tetra
Neon tetras are small schooling fish from the blackwater tributaries of the western Amazon basin. In their natural habitat, the water is very soft, acidic, and tannin-stained — conditions quite different from the harder, more alkaline tap water common in many Polish cities.
Neon Tetra — Parameters
- Temperature: 20–26 °C
- pH: 6.0–7.0 (tolerates up to 7.5 with gradual acclimation)
- GH: 1–10 dGH (soft to moderately hard)
- Minimum school size: 8–10 individuals
- Tank volume: 60 litres minimum for a school
- Diet: Small granules, micro-pellets, frozen Artemia, Daphnia
In very hard tap water (GH above 15 dGH), neon tetras tend to show reduced colour and diminished spawning activity over time. Mixing reverse osmosis water with tap water to achieve a GH between 5 and 10 dGH, and a pH around 6.5–7.0, replicates conditions closer to their native range and supports better long-term condition.
Neon tetras are peaceful and compatible with other small, non-predatory species. They should not be housed with fish large enough to consume them — including adult Angelfish, which despite frequent marketing as community fish are capable of eating small tetras.
Bottom Dwellers
Corydoras paleatus — Peppered Corydoras
Corydoras paleatus originates from temperate river systems in southern Brazil and Argentina, and notably tolerates water temperatures down to 18 °C. This makes it one of the few tropical fish genuinely suited to tanks without consistent heating — useful in setups where room temperature during Polish winters does not drop below 17–18 °C.
Corydoras paleatus — Parameters
- Temperature: 18–26 °C
- pH: 6.0–8.0 (broadly tolerant)
- GH: 2–20 dGH
- Minimum group size: 4–6 (social species, distressed when alone)
- Substrate: Fine sand recommended — sharp gravel damages barbels
- Diet: Sinking pellets, frozen bloodworm, blanched vegetables, scavenging leftover food
Corydoras breathe atmospheric air periodically — they swim rapidly to the surface, gulp air, and return to the bottom. This is a normal respiratory behaviour and does not indicate oxygen deficiency. However, if this behaviour becomes very frequent, it may indicate elevated CO₂ or insufficient dissolved oxygen in the water column.
Sharp gravel substrate causes progressive damage to the sensitive barbels around the corydoras mouth. Over months, barbels shorten and may become infected. Fine sand or rounded river gravel eliminates this risk.
Livebearers
Xiphophorus hellerii — Swordtail
Swordtails are hardy livebearers from Central America, with a natural distribution extending from Mexico to Honduras. Males develop an elongated lower tail fin (the "sword") and are notably territorial toward other males of their species, though they generally ignore fish of different appearance.
Swordtail — Parameters
- Temperature: 22–28 °C
- pH: 7.0–8.3
- GH: 10–20 dGH (prefers harder water)
- Minimum tank: 80 litres for a group with multiple males
- Diet: Flake food, pellets, occasional live/frozen invertebrates, vegetable matter
- Note: Prolific breeders — expect fry regularly in a mixed-sex group
Swordtails are well suited to the harder, more alkaline tap water found in many Polish cities. Their GH preferences align closely with typical municipal water parameters, reducing the need for water modification. They are commonly stocked as a straightforward introductory species for new aquarists.
Compatibility Principles
When assembling a community tank, the following factors determine whether species coexist without chronic stress:
Water parameter overlap
All species in the same tank should be able to thrive at the same temperature, pH, and hardness. Mixing soft-water species with hard-water species is possible if both tolerate mid-range values, but neither group will be at its best long-term. Dedicated soft-water tanks or hard-water tanks produce more stable results.
Size differential
Any fish that fits entirely in another fish's mouth may be consumed. This rule applies regardless of species reputation — even ostensibly peaceful fish will eat small fish if opportunity arises. Keeping fish within a similar size range (no more than a 3:1 ratio in body length) reduces predation risk.
Fin-nipping
Certain species — tiger barbs being the most frequently cited example — nip the fins of slow-moving or long-finned fish. Betta splendens, angelfish, and male guppies with long tails are vulnerable. These combinations should be avoided in community setups.
Feeding
Most community fish do well on a varied diet of dry food (flakes or pellets as a staple) supplemented with frozen or live invertebrates two to three times per week. Frozen bloodworm (chironomid larvae), Daphnia, and brine shrimp (Artemia) are widely available in Polish aquarium shops and through online suppliers.
Overfeeding is a common cause of water quality problems in home aquariums. A useful indicator: feed only what the fish consume within two to three minutes, twice daily. Uneaten food should be removed with a siphon or pipette before it decomposes.
Related reading: Aquarium Setup Guide covers filtration and the nitrogen cycle. Aquatic Plants Guide describes which plant species coexist with active or burrowing fish.
Parameter data sourced from FishBase. Last updated 4 June 2026.