Molly Stocking
Minimum 20 gal · 4" adult · medium bioload · peaceful.
Estimated bioload
204%
overstocked
Bioload-based: it weighs adult size and waste output, not the oversimplified "1 inch per gallon" rule.
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Keeping Molly
The Molly grows to about 4 inches and needs a minimum of 20 gallons. Its bioload is medium, meaning it produces a moderate amount of waste for its size, a key factor the "one inch per gallon" rule ignores. It's a schooling species, so keep at least 3 together or they'll be stressed. Temperament is peaceful, making it a good community fish. Use the calculator above to see how a group fits your tank's real volume before you buy.
Frequently asked questions
What size tank does a Molly need?
At least 20 gallons. They're a schooling fish, so keep a group of 3 or more.
Is the Molly peaceful?
Temperament is peaceful. Reaching about 4" as an adult with a medium bioload, plan tankmates and filtration accordingly.
Keep going with the same pet
Not sure of your tank's exact gallons? Measure it with the aquarium volume calculator first.
Your dog's age in human years, breed-size adjusted, not the ×7 myth.
Your cat's age in human years using the real feline curve, not the ×7 myth.
How much to feed: daily calories and cups by weight, activity and life stage.
Tank gallons and liters from your dimensions: rectangle, cylinder, hex and more.