Can a guppy live with neon tetras?

Sometimes, with care.

pH ranges only just overlap (7.0–7.0), so one of them will be outside its comfort zone if your water drifts.

Plan on a tank of at least 10 gallons for both.

By tank size

Below 10 gallons there isn’t enough room for both, so the answer is no.

How to try it

Use a 10-gallon tank at the very least, and go larger if you can, since you need room for a group of at least 6 neon tetras plus at least 3 guppies (several females to each male). Choose a tank that has already cycled and matured, because neons don't cope with new-tank swings, and add plenty of plants so both species have cover. Keep the temperature at 72–77°F, where both are comfortable.

1. Test your tap water for pH and GH before buying any fish. Neons prefer softer water (1–11 dGH) and guppies prefer harder water (9–20 dGH), so you want a reading in the overlap, around 9–11 dGH. Your pH should sit right at 7.0.
2. Make sure the tank is fully cycled and mature, with ammonia and nitrite at zero, and set the heater to 72–77°F.
3. Add the neon tetras first, all 6 or more together, and let them settle for a couple of weeks while you keep checking pH and GH.
4. Add the guppies next, starting with a group of at least 3 and keeping several females to each male.
5. Feed small amounts twice a day for the first weeks, and test water parameters every few days until they stay stable.

Warning signs in the first weeks

• Neons that clamp their fins, lose colour, hide constantly or hover near the bottom. This can mean the water is too hard or the pH has drifted out of their range.
• Guppies that look pale, listless or stressed if pH slips below 7.0, because that is the bottom of their range.
• Neons that stop schooling and scatter, or any fish being chased, especially males harassing females if you have too few of them.
• Fish gasping, flashing or showing white patches soon after the move, which can be a sign that parameters are swinging.

Backup plan: If the neons or guppies stay stressed after you have checked and stabilised pH and GH, separate them. Move one species to its own tank, ideally the neons into softer, slightly more acidic water, or the guppies into harder water.

How we reached this verdict

Side by side

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