Beginner answer
Compatible freshwater fish share temperature, pH, tank size, temperament, and feeding pace. Start with the concrete limits: tank volume, adult size, temperament, group size, water range, and filtration margin.
Top compatibility checks
- Same temperature range - Tropical fish usually need 72-82 F; mixing coldwater and tropical fish causes chronic stress.
- Similar aggression level - Peaceful fish belong with peaceful fish; avoid fin-nippers with bettas, guppies, or angelfish.
- Matching pH range - Most community fish tolerate pH 6.5-7.5, but sensitive species still need stable water.
- Appropriate tank size - Use the larger species minimum, not the smaller fish minimum.
- Schooling group size - Neon tetras, rasboras, and Corydoras show stress when kept alone.
Setup rule: A safe result means the pairing is commonly workable under normal aquarium conditions. Risky means setup details matter. Avoid means there is a clear beginner-level conflict.
Setup rule: If the data is low confidence, the tool should show Needs more research instead of pretending to know.
How to use this calculator
Use this as a first-pass pair check, then confirm that both species also fit the same tank size, water range, and adult behavior.
Pay extra attention to fin nipping, predation, temperature mismatch, and confidence level; those are the usual hidden problems.
If a pair is caution or needs more research, check the species guide and plan a backup before mixing them.
Warnings
These are the failure points that hurt beginner tanks most often. Do not use any calculator as a replacement for water testing, quarantine, observation, or experienced care judgment. The result is a planning screen, not a guarantee.
- Tiger barbs - Confirmed fin-nippers; do not keep them with bettas, angelfish, guppies, or other long-finned fish.
- Goldfish - Coldwater, high-waste fish that do not belong with warm tropical community species.
- Angelfish - Adults become territorial and may eat very small fish such as neon tetras in cramped tanks.
- Pea puffers - Aggressive hunters that bite fins and attack snails; treat them as species-only unless experienced.
- Temperature mismatch - White cloud mountain minnows and goldfish prefer cooler water than bettas and many tropical fish.
Editorial notes
How this page is maintained: Tool pages explain the calculator logic and its limits. The rules favor readable warnings over fake precision, especially when stocking or compatibility depends on setup details.
This page uses conservative local care data, explicit compatibility records, and established aquarium care references rather than store-label shorthand.
Combinations are reviewed before they are promoted as indexed guides, and uncertain pairs stay cautious or marked as needing more research.
The recommendations are intentionally conservative because most readers are planning beginner tanks, where water quality and backup options are limited.
Last reviewed: 2026-06-30.