Neon tetras and guppies are usually peaceful enough to live together, but the pairing is not perfect on paper because their typical hardness preferences differ. Neon tetras need a proper school, while mixed-sex guppies can multiply quickly. Test your source water, avoid extreme chemistry for either species and plan for the adult population rather than the first-day headcount.
When two peaceful species are combined, fishkeepers often stop at behaviour. With guppies and neon tetras, water hardness and future stocking are at least as important as aggression.
The behavioural fit is generally good
Both species are small community fish and serious territorial conflict is uncommon in a properly sized aquarium.
Compare hardness, not just temperature
Guppies usually favour harder mineral-rich water, while neon tetras are associated with softer conditions. Many captive-bred fish tolerate overlap, but the source water should still be measured rather than guessed.
Keep the neon school properly
The RSPCA classifies tetras as shoaling fish and recommends groups of six or more. Do not reduce the tetra group simply to make room for more guppies.
Account for guppy fry
A mixed-sex guppy group can increase the bioload quickly. Leave room for population growth or use a deliberate sex plan.
Related aquarium tools and guides
Frequently asked questions
Will guppies bully neon tetras?
Usually not, although feeding competition can occur.
Which water parameter matters most?
GH is especially useful because the species often prefer different mineral levels.
Can I keep only a few neon tetras with guppies?
No. Neon tetras still need a proper social school.
Sources and further reading
This guide separates general aquarium arithmetic from fish-welfare decisions. For species-specific limits, always check the needs of the fish you intend to keep.