Black molly Poecilia sphenops

Read the hardness column and then read every other column, because the contrast is the point. Hardness is unanimous and nothing else is. The tank runs from 10 gallons to about 21, a factor of two. The adult size runs from 3.1 inches to 7, though the 7 belongs to a different species. The pH floor moves half a point. The lifespan appears on two sources of four.

The tank column disagrees about what the number is for rather than about the fish. Fishkeeping World gives the arithmetic openly: 10 gallons for up to four mollies, followed by 3 gallons per extra molly fish. Store Depot says the fish is kept in tanks as small as 15 gallons and then recommends something else, that a 20 gallon long is a good candidate to start with. Seriously Fish gives a 36 by 12 inch base, about 21 gallons. Both sources that describe a tank rather than a minimum land on twenty, so twenty is the row.

The size column is the one the label ruins. Seriously Fish caps this fish at 80 mm standard length, 3.1 inches. Wikipedia gives 8.4 cm, 3.3 in, standard length or 10 cm, 3.9 in, total length, but is usually smaller. Fishkeeping World gives up to 4.5 inches. Store Depot gives the range for the word rather than the fish: adult mollies vary from a little over 3 inches, right up to about 7 inches in length. The seven inch fish is the giant sailfin Poecilia velifera, a different species sold under the same name, so this row stops at 4.5.

Two figures agree with our own relatives here and are worth putting side by side. Our guppy record publishes 143 to 536 ppm, and 536 is the same 30 dGH ceiling, so the two Poecilia records on this site agree on the top of the hardness range to the ppm and differ by nearly double at the bottom. On lifespan the order runs the other way: guppy 2 to 3 years, our platy record 1 to 5, and this record 3 to 5, which makes the molly the longest lived livebearer we publish.

Seriously Fish, on the same page as its freshwater figures: the species is a popular choice to cycle new marine aquariums and can live a happy life in full marine conditions. Wikipedia, on the species: P. sphenops inhabits freshwater and brackish habitats. Fresh and brackish, with marine absent.

Neither is wrong, and they are not answering the same question. Seriously Fish is describing the outer limit of what the animal will tolerate, which is a real fact and the reason the fish is used to cycle marine tanks. Wikipedia is describing the habitats the species actually occupies in the wild, which is a different measurement. A fish can tolerate more than it inhabits, and on this species the gap between the two is the whole of the ocean.

This is the first record on this site whose source claims an animal can live in full marine conditions. Five other records mention brackish water and none goes further: our least killifish, java fern, java moss, ghost shrimp and nerite snail records.

The useful source here is the third one, because it separates two ideas that a shopper will otherwise merge. Aquarium Store Depot: the salt these fish require does not necessarily need to be regular aquarium salt, NaCl. Calcium and magnesium are essential. That is the difference between hardness and salinity, and it is the difference between a molly tank that works and one that has quietly excluded every other fish in it.

Hard water means dissolved calcium and magnesium, which is what the unanimous 15 to 30 dGH row is measuring. Salt means sodium chloride, which raises nothing on that scale. A keeper who reads full marine conditions and adds a bag of aquarium salt has not raised the hardness and has ruled out most tank mates, and no source we hold recommends that route for a freshwater tank.

So this record answers the question in the direction the keeper needs. The molly is a hard water fish, the hardness is calcium and magnesium, and the marine tolerance is a fact about the animal rather than an instruction about the tank. Crushed coral or a mineral supplement is in the kit list above for that reason.

On appearance, Fishkeeping World is the only source that describes the black form rather than the species: black mollies, the most common molly fish type, have all-black bodies and rounded fins. Of mollies generally it says most mollies are between 3.5 and 4.5 inches in length, with flattened bodies and short fins.

And on the same page it gives the black molly a different size from the one it gives mollies, describing them as running between three and six inches. Six inches is above its own general figure of 4.5 and above every other source we hold: Seriously Fish caps the species at 3.1 inches and Wikipedia at 3.9 total length. The row on this record stays at 3.1 to 4.5, and the six inch figure is named here rather than used, because a source disagreeing with itself on one page is not a fifth opinion.

The fins are also how you sex the fish, and two sources describe the same structure with one of them naming it. Fishkeeping World: the anal fin on a male common molly is long and points backward, while the anal fin on a female common molly points down. Seriously Fish names what that long backward-pointing fin is: the male is smaller, more colourful and possesses a gonopodium. Wikipedia adds the size direction, that females grow about a centimeter larger than males, which is the opposite of most people’s expectation.

On plants, Fishkeeping World names two species and this site holds a record for both. Tall plants like anubias nana and short varieties like Java fern provide shelter and a hiding place for molly fish, with rocks and caves to escape to if the fish are being hassled. Our anubias record covers the nana form and our java fern record publishes pH 6.0 to 7.5, which stops where this record’s pH row starts, so the plant is named by a source and argued with by our own rows. Substrate is a thin layer of sandy substrate to hold the plants, and a filter is required to remove ammonia, nitrate and debris.

On health, Fishkeeping World names three conditions and every one of them has a water or stress cause rather than a molly-specific one. Ich: white spots, which look like salt sprinkles, on the fish’s fins, body, and tail, with the fish lethargic and rubbing against rough surfaces. Velvet: the parasite burrows into the fish’s skin and produces gold, rust-like cysts, and the fish darts from one end of the tank to the other. Fin and tail rot: caused by a bacterial infection resulting from overcrowding, poor-quality water, and stress, leaving fins frayed, ragged, and milky-colored.

Read those three causes against station 01 and the loop closes. Two of the three are named as consequences of water quality and stress, and the water this fish needs is the hardest any record here asks for, which is exactly the parameter a keeper in soft tap water is most likely to get wrong and least likely to test. No source we hold names a disease specific to mollies, so this record does not print one.