What mollies really cost
Every figure on this page is for a group of 4 mollies.
Costs for 4 fish:$1,200 lifetime$550 first year$230 a year afterBreakdown
Four mollies cost only about $20–$52, but they grow to 3–5 inches and Petco wants 30 gallons, so the real cost is a 29-gallon kit on a stand: with gravel, plants and test strips it typically runs about $320. After that, expect around $225 a year, more than a third of it electricity to heat 29 gallons, plus food, filter cartridges, a heater every year or two and the odd medication. Keep males and females together and you will also have fry to deal with roughly monthly.
- Life expectancy
- 2–5 years
- Size
- About 3–5 in; females larger than males, sailfins larger still
- Care level
- Low
- Price, for 4 fish
- $20–$52
- Setup
- About $320
- Insurance
- Not offered
Estimate for: A group of 4 mollies (1 male, 3 females) in a heated, filtered 29-gallon tank on a stand; prices cover the whole group. Space needed: A 29-gallon tank with lid, heater (72–82°F) and filter; Petco lists 30 gallons as the minimum and PetMD wants 30+ for sailfins.
Lifetime cost, for 4 fish$1,200
First year $550Then about $230 a year
Where the money goes each year
A typical year for a group of 4 mollies, with typical spending in an average-cost area.
- Electricity for heater and filter$81
- Spirulina flakes plus freeze-dried treats$39
- Filter cartridges$32
- Illness and injury (average)$25
- Replacement heater (100 W)$22
- Test strips$13
- Plant and decor refresh$10
- Water conditioner refill$4
- Typical year$230
Most years land between $140 and $370. Items replaced on a cycle are spread across the years.
Setup and the first year
For mollies, the equipment costs far more than the animal.
Bringing them home
- Price: Pet store (PetSmart, Petco, local fish store), group of 4$36
- 29-gallon aquarium kit (tank, hood with LED, filter, heater, thermometer)$132
- Aquarium stand for a 29-gallon tank$104
- Gravel or sand$32
- Live plants (cover for fry, extra grazing)$20
- Water conditioner (first bottle)$8
- Water test strips$13
- Gravel vacuum (siphon)$8
- To bring them home$350
Running costs in year one
- Spirulina flakes plus freeze-dried treats$39
- Filter cartridges$32
- Test strips$13
- Electricity for heater and filter$81
- Plant and decor refresh$10
- Illness and injury (average)$25
- Year-one running costs$200
First-year total: $550.
Make it your estimate
Change the choices that move the price most. Totals update as you go.
Your lifetime estimate$1,200
First year $550Then about $230 a yearOver 4 years
$19 a month in a typical year.
Show your yearly breakdown
- Electricity for heater and filter$81
- Spirulina flakes plus freeze-dried treats$39
- Filter cartridges$32
- Illness and injury (average)$25
- Replacement heater (100 W)$22
- Test strips$13
- Plant and decor refresh$10
- Water conditioner refill$4
- Typical year$230
What to buy
The gear and supplies in this estimate, matched to a group of 4 mollies. Each link searches Amazon for the right type and size.
- 29-gallon aquarium kit (tank, hood with LED, filter, heater, thermometer)Setup, typically about $132See on Amazon
- Aquarium stand for a 29-gallon tankSetup, typically about $104See on Amazon
- Gravel or sandSetup, typically about $32See on Amazon
- Live plants (cover for fry, extra grazing)Setup, typically about $20See on Amazon
- Water conditioner (first bottle)Setup, typically about $8See on Amazon
- Water test stripsSetup, typically about $13See on Amazon
- Gravel vacuum (siphon)Setup, typically about $8See on Amazon
- Spirulina flakes plus freeze-dried treatsOngoing, typically about $39 a yearSee on Amazon
- Filter cartridgesOngoing, typically about $32 a yearSee on Amazon
- Replacement heater (100 W)Ongoing, typically about $33 each, every 1.5 yearsSee on Amazon
As an Amazon Associate, PetPriceTag earns from qualifying purchases. Buying through these links costs you nothing extra and never changes our cost figures.
Health costs to plan for
| Condition | What it is | Typical treatment | Cost |
|---|---|---|---|
| Ich (white spot disease) | A contagious protozoan parasite, usually brought in with new fish; white specks, flashing against decor and lethargy. Listed by both PetMD and Chewy among common molly problems. Source | Ich medication for the whole tank (API Super Ick Cure 2 × 4 oz, $12.58) and a water change; a mobile fish vet tank visit is about $200 plus mileage | $13–$213 |
| Shimmying ("molly disease") | Shimmying is a warning sign Chewy lists for molly disease, ich, velvet and fin rot; its first-step advice is to test the water, do a water change and add some salt, and it stresses that mollies need hard water. Source | Test the water, change it with a gravel vacuum and add salt as Chewy advises (API aquarium salt 65 oz, $12.48); crushed coral if water is soft | $12–$25 |
| Dropsy | Fluid buildup with pinecone-like raised scales, a sign of organ failure, infection or chronic stress from poor water; severe cases are often fatal. Source | Better water and antibiotics or raised salinity under veterinary guidance; a mobile fish vet tank visit is about $200 plus mileage | $0–$200 |
| Fungal and water-mold infections | Cottony white-to-brown patches that follow injury, poor water, overcrowding or aggression; PetMD lists fungal infections among common molly problems. Source | Fix water quality and crowding, then measured aquarium salt (about 1–2 g/L; API 65 oz, $12.48); vet diagnosis recommended before treating | $12–$213 |
The yearly estimate includes an average of $25 for illness and injury. Mainstream U.S. pet insurers do not cover aquarium fish; exotic-pet policies such as Nationwide's avian and exotic plan are aimed at birds, reptiles and small mammals. Budget for medications and the rare fish-vet visit yourself.
What drives the cost
- Tank advice ranges from 20 to 30 gallons: Chewy's care sheet says at least 20, PetMD says two mollies fit in 10 gallons plus 3 per extra fish but sailfins need 30+, and Petco's listings say 30. We price a 29-gallon kit, the standard size closest to 30, plus a stand to hold its weight.
- Mollies breed constantly. FishBase records 20–150 young after a 28-day gestation, and Petco warns a tank can grow quickly once males and females are together. PetMD's one-male-to-three-females group will produce fry; plan to rehome them or keep live plants so a few survive. An all-male group, which Chewy says works, avoids fry.
- Electricity is the biggest yearly cost: holding 29 gallons about 10°F above room temperature plus a filter averages roughly 50 W, about $81 a year at the July 2026 U.S. average rate. A cold room can nearly double it.
- Mollies want hard, alkaline water (Petco lists pH 7–8.3 and 12–30 dKH). Chewy suggests crushed coral or limestone decor if your tap water is soft, which this estimate does not price.
- Medications are cheap; vets are not. A two-bottle pack of ich treatment is $12.58 at Chewy, while a mobile fish vet's tank visit runs about $200 plus mileage at California Fish Vet.
Is it legal where you live?
Mollies are legal to own throughout the U.S. and sold at national chains; they are not on the federal injurious-wildlife list. Never release them or surplus fry into the wild.
Cities and counties can have their own rules. Check locally before you buy.
- Pet store (PetSmart, Petco, local fish store), group of 4
- $20–$52
- Lifetime
- $1,200
How this estimate is built
Every line, with the typical, thrifty and generous figures and where each comes from.
Show all 15 line items and their sources
| Item | Typical | Basis and sources | |
|---|---|---|---|
| Setup | |||
| 29-gallon aquarium kit (tank, hood with LED, filter, heater, thermometer) | $132 | Top Fin Essentials 29-gal starter kit (30.2 x 12.4 x 21.9 in) with hood, LED, filter, heater, thermometer, net and test vial: $131.99 on sale at PetSmart (20% off 20+ gallon kits), $164.99 regular (high). The comparable Aqueon 29-gal LED kit (QuietFlow 20 filter, 100 W heater) is $159.99. Gravel and plants not included. PetSmart: Top Fin Essentials Aquarium Starter Kit, 29 gal ($131.99 sale, $164.99 regular); That Pet Place: Aqueon LED Aquarium Kit, 29 gallon ($159.99; QuietFlow 20 filter, 100 W heater) | |
| Aquarium stand for a 29-gallon tank | $104 | A full 29-gallon tank weighs a few hundred pounds, so it needs a stand or furniture rated for it. Typical: TitanEze steel stand for 11–30 gal tanks, from $104.39 at PetSmart. High: Top Fin Bourbon Oak 20–37 gal cabinet, $179.99. Low: $0 if you already own furniture rated for the weight. PetSmart: aquarium stands (TitanEze 11–30 gal from $104.39, Top Fin Bourbon Oak 20–37 gal $179.99) | |
| Gravel or sand | $32 | Chewy's molly care sheet lists CaribSea gravel 20 lb at $15.96 and CaribSea sand 20 lb at $23.79. Typical: two bags of gravel for a 30 x 12 in footprint; low: one bag for a thin layer; high: two bags of sand. Bag counts are our estimate. Chewy: Molly Fish Care Sheet (20-gallon minimum, 3–5 per group, hard water, product prices) | |
| Live plants (cover for fry, extra grazing) | $20 | Chewy notes live plants give fry places to hide and help keep water clean. Java fern is $9.99 at Aquarium Co-op; one plant low, two typical, four high. Chewy: Molly Fish Care Sheet (20-gallon minimum, 3–5 per group, hard water, product prices); Aquarium Co-op: Java Fern ($9.99) | |
| Water conditioner (first bottle) | $8 | API Stress Coat 8 oz, $7.69 at Chewy (5 ml per 10 gallons; treats up to 470 gallons). Chewy: API Stress Coat Aquarium Water Conditioner, 8 oz ($7.69; 5 ml per 10 gal; treats 470 gal) | |
| Water test strips | $13 | Needed to watch nitrite and nitrate while the tank cycles and to check hardness and pH, which mollies are sensitive to. API 5-in-1 strips at Chewy: 25 ct $12.98 (typical), 4 ct $6.98 (low), 100 ct $24.98 (high). They do not test ammonia. Chewy: API 5 in 1 Aquarium Test Strips (4 ct $6.98, 25 ct $12.98, 100 ct $24.98) | |
| Gravel vacuum (siphon) | $8 | Chewy's molly care sheet lists a SunGrow siphon vacuum at $7.70 and an Aqueon siphon vacuum with priming bulb at $19.79 (high). The kit includes a net. Chewy: Molly Fish Care Sheet (20-gallon minimum, 3–5 per group, hard water, product prices) | |
| Every year | |||
| Spirulina flakes plus freeze-dried treats | $39 | PetMD and Chewy describe mollies as omnivores that should eat mostly plant-based food with some protein, fed 1–3 times a day. Chewy's sheet prices Zoo Med Spirulina 20 (4 oz) at $12.99, Aqua Natural freeze-dried daphnia (0.7 oz) at $6.49 and Ocean Nutrition Brine Shrimp Plus flakes (2.5 oz) at $12.96. We assume opened food is replaced about every six months. Low: 2 spirulina = $25.98. Typical: 2 spirulina + 2 daphnia = $38.96. High: 2 spirulina + 2 brine shrimp flakes + 4 daphnia = $77.86. Chewy: Molly Fish Care Sheet (20-gallon minimum, 3–5 per group, hard water, product prices); PetMD: Molly Fish Care Sheet (Ivan Alfonso, DVM) | |
| Water conditioner refill | $8 every 2 years | PetMD advises changing 10–25% of the water every 2–4 weeks. At 25% every two weeks, 29 gallons need about 190 gallons of new water a year; at 5 ml per 10 gallons that is about 95 ml, so an 8 oz bottle ($7.69, treats 470 gallons) lasts about two years. PetMD: Molly Fish Care Sheet (Ivan Alfonso, DVM); Chewy: API Stress Coat Aquarium Water Conditioner, 8 oz ($7.69; 5 ml per 10 gal; treats 470 gal) | |
| Filter cartridges | $32 | Top Fin Silenstream large cartridges (fit the 20–75 gal Silenstream filters) are $15.99 per 6-pack at PetSmart. PetMD advises a full tank cleaning about monthly, so we assume a cartridge a month, two packs a year. Low: one pack, rinsing cartridges in tank water between changes. PetSmart doesn't name the kit's filter model, so check the cartridge size before buying. PetSmart: Top Fin Silenstream Large Filter Cartridges, 6 ct ($15.99; fit 20–75 gal Silenstream filters); PetMD: Molly Fish Care Sheet (Ivan Alfonso, DVM) | |
| Test strips | $13 | One 25-count pack of API 5-in-1 strips a year for testing every two weeks ($12.98 at Chewy). Low 4 ct $6.98; high 100 ct $24.98 for weekly testing. Chewy: API 5 in 1 Aquarium Test Strips (4 ct $6.98, 25 ct $12.98, 100 ct $24.98) | |
| Replacement heater (100 W) | $33 every 1.5 years | Chewy recommends 3–5 W per gallon for mollies, so about 100 W for 29 gallons. Bulk Reef Supply advises replacing heaters every 1–2 years, and $30–$40 heaters yearly, because a stuck heater can cook or chill the fish; modeled every 1.5 years. Typical and low: Marineland 100 W, $32.97; high: Fluval M 100 W, $35.99 (both listed on Chewy's molly care sheet). Chewy: Molly Fish Care Sheet (20-gallon minimum, 3–5 per group, hard water, product prices); Bulk Reef Supply: 5-Minute Aquarium Guide Ep. 12, Heaters (replace every 1–2 years; $30–$40 heaters yearly) | |
| Electricity for heater and filter | $81 | Rough estimate. AquariumScience.org figures 'very roughly' 1.5 W per gallon to hold water 10°F above room temperature, so a 29-gallon heater averages ~43.5 W; the filter is taken as 7 W (an AquaClear 50's rating at 120 V; PetSmart doesn't give the kit filter's). 50.5 W × 8,760 h = 442 kWh × $0.1831/kWh (EIA U.S. residential average, July 2026) = $81.00. Low: 5°F rise = 28.75 W = $46.11. High: 20°F rise in a cold room = 94 W = $150.77. The LED light is not counted. U.S. EIA Electric Power Monthly: average residential price, July 2026 (18.31 cents/kWh); AquariumScience.org: Aquarium electric cost (heater ~1.5 W per gallon for a 10°F rise); Aquarium Depot: Fluval AquaClear AC50 power filter (20–50 gal, 200 gph, 7 W at 120 V) | |
| Plant and decor refresh | $10 | Mollies graze on plants and algae, so a plant or two may need replacing (java fern $9.99 at Aquarium Co-op). Many owners spend nothing. Aquarium Co-op: Java Fern ($9.99) | |
| Illness and injury, per year | |||
| Fish medications (and the rare vet visit) | $25 | Most molly illness is treated at home for the whole tank. Typical: a two-bottle pack of API Super Ick Cure ($12.58 at Chewy) plus API freshwater aquarium salt 65 oz ($12.48, listed on Chewy's molly care sheet) = $25.06. High adds one mobile fish vet tank visit, about $200 plus mileage at California Fish Vet (water testing and sedated exams of up to 3 fish). Few owners take $5 fish to a vet. Chewy: API Liquid Super Ick Cure, 4 oz, bundle of 2 ($12.58); Chewy: Molly Fish Care Sheet (20-gallon minimum, 3–5 per group, hard water, product prices); California Fish Vet (Jessie Sanders, DVM): Fish Veterinary Services (tank package about $200 plus mileage) | |
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Common questions
How much do mollies cost?
For a group of 4 mollies: Pet store (PetSmart, Petco, local fish store), group of 4: $20–$52. The bigger costs come after: about $320 to set up, about $550 for the whole first year, then about $230 a year.
How much do mollies cost per year?
For a group of 4 mollies: About $230 a year ($19 a month) for a typical owner in an average-cost area, ranging from about $140 for a thrifty owner in a lower-cost area to $370 for a generous owner in a big city.
How much do mollies cost over their lifetime?
For a group of 4 mollies: About $1,200 over a 4-year life, in 2026 dollars.
Sources
- PetMD: Molly Fish Care Sheet (Ivan Alfonso, DVM)
- Chewy: Molly Fish Care Sheet (20-gallon minimum, 3–5 per group, hard water, product prices)
- FishBase: Poecilia sphenops, Molly (20–150 young after a 28-day gestation)
- Petco: Black Molly ($4.99; 30-gallon minimum tank; up to 5 in; livebearer)
- PetSmart: Molly fish listing (Calico Lyretail Molly $5.49; buy 4, get the 5th free on community fish)
- U.S. EIA Electric Power Monthly: average residential price, July 2026 (18.31 cents/kWh)
- California Fish Vet (Jessie Sanders, DVM): Fish Veterinary Services (tank package about $200 plus mileage)
- Petco: Dalmatian Lyretail Molly ($5.99; 30-gallon minimum tank)
- Aquatics Unlimited: Mollies (Black and Sailfin $4.99–$19.99, balloon and lyretail varieties $8.99–$12.99)
- PetMD: Dropsy in Fish (Jessie Sanders, DVM, DABVP Fish Practice)
- PetMD: Fungal Infections in Fish (Jessie Sanders, DVM, DABVP Fish Practice)
- PetSmart: Top Fin Essentials Aquarium Starter Kit, 29 gal ($131.99 sale, $164.99 regular)
- That Pet Place: Aqueon LED Aquarium Kit, 29 gallon ($159.99; QuietFlow 20 filter, 100 W heater)
- PetSmart: aquarium stands (TitanEze 11–30 gal from $104.39, Top Fin Bourbon Oak 20–37 gal $179.99)
- Aquarium Co-op: Java Fern ($9.99)
- Chewy: API Stress Coat Aquarium Water Conditioner, 8 oz ($7.69; 5 ml per 10 gal; treats 470 gal)
- Chewy: API 5 in 1 Aquarium Test Strips (4 ct $6.98, 25 ct $12.98, 100 ct $24.98)
- PetSmart: Top Fin Silenstream Large Filter Cartridges, 6 ct ($15.99; fit 20–75 gal Silenstream filters)
- Bulk Reef Supply: 5-Minute Aquarium Guide Ep. 12, Heaters (replace every 1–2 years; $30–$40 heaters yearly)
- AquariumScience.org: Aquarium electric cost (heater ~1.5 W per gallon for a 10°F rise)
- Aquarium Depot: Fluval AquaClear AC50 power filter (20–50 gal, 200 gph, 7 W at 120 V)
- Chewy: API Liquid Super Ick Cure, 4 oz, bundle of 2 ($12.58)
- eCFR: 50 CFR 16.13, injurious fish, mollusks and crustaceans
Estimates in 2026 US dollars. Vet prices for this pet use the same region adjustment as the rest of the site (methodology). Updated October 17, 2026. Spot a wrong figure?