Can Cardinal Tetra Live With Molly?
No, cardinal tetras and mollies want opposite water chemistry, with cardinals needing soft acidic conditions and mollies requiring hard alkaline water.
Why
- Cardinal tetras need pH 5.0-7.0 and thrive in soft, acidic blackwater with tannins and low hardness.
- Mollies prefer pH 7.5-8.5 and do best in hard, alkaline water, often with salt added.
- The pH overlap sits at exactly 7.0, which is too alkaline for wild-caught cardinals and too soft for mollies.
- Mollies grow to 4-5 inches and stay active at the surface, outcompeting 2-inch cardinals for food.
- Mollies are surface-feeders that dart and push at feeding time, leaving skittish cardinals stressed and underfed.
What could go wrong
Cardinals fade, stop schooling, and die over weeks as their osmoregulation struggles in hard water, while mollies shimmy and get sick in acidic conditions.
If you keep them in separate tanks
Sized for the 20 gallon minimum this pairing needs. Affiliate links — we earn a small commission if you buy through them.
AquaClear 30 Power Filter
Oversized filtration is what lets you stock two species together without water quality crashing. Rated for a tank slightly larger than the 20 gallon minimum.
Eheim Jager 150W Thermostat Heater
Holds a steady temperature inside the 73-81°F window both species need.
API Freshwater Master Test Kit
Keep ammonia, nitrite, and nitrate in check. Two-species tanks have more bioload and less margin for error than single-species setups.
Better pairings to consider
Cardinals do well with neon tetras, rummy nose tetras, or harlequin rasboras in soft acidic water. Mollies thrive with platies, swordtails, or bristlenose plecos in hard alkaline water.
Related compatibility questions
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