Mollies Need Salt!

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A stroke of the brush does not guarantee art from
Jul 16, 2005
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Berkhamsted, Hertfordshire, England
You'll often here experienced aquarists insist you add salt to your aquarium for the benefit of the mollies. Why is this?

The Background

The mollies you are most likely to buy at the pet store are hybrids. Black mollies, golden mollies, veiltail mollies, balloon mollies, and all the others are all hybrids created by careful cross-breeding of two or more species. Some molly species live in fresh water, while others live in brackish water. There's usually a little of both kind in any given aquarium strain.

The Problem

When mollies are kept in freshwater tanks, they often become sickly. Common symptoms are fin-rot, fungus, and the "shimmies". Fin-rot is a gradual decay of the fins, often with obviously dead, grey patches on the fins. Left untreated, this will kill your fish. Fungus usually looks like fine white threads and can appear anywhere on the body, though it's most common on the fins. Again, untreated, this is serious. Both fin-rot and fungus are easily treated with over-the-counter fish medicines. The shimmies are, as the name suggests, a bit like the dance of the same name. The fish seem to tread water, wobbling from side to side. Yet again, left untreated, this will kill your fish.

The Solution

Add marine aquarium salt mix. This will turn your tank into a slightly brackish rather than freshwater aquarium and the mollies will be much healthier. Fin-rot and fungus will not set in, and if present, should fix themselves, especially if you treat with the appropriate remedy as well. The shimmies usually go away.

You don't need a lot of salt, around 3-5 grammes per litre will do the trick. Use a hydrometer to measure the specific gravity (the concentration of salt in the water). You are aiming for a specific gravity of about 1.003 to 1.005. Don't add the salt to the aquarium directly! Make up some salty water in a bucket, and then pour it into the tank. Be sure and follow the instructions on the package with regard to how long you need to stir the salt into the water for, etc.

The salt doesn't just make the aquarium salty, it also raises the pH and hardness, which is just as critical for mollies.

Note that table salt and aquarium tonic salt aren't acceptable alternatives. Always use marine aquarium salt. It isn't expensive, particularly not in the small amounts needed for keeping mollies.

Pros & Cons of Salty Water

Most other livebearers will be fine in slightly brackish water, so don't worry about things like guppies and platies. However, most freshwater fish don't like salty water, especially not things like tetras and Corydoras. Mollies basically aren't an option for aquarists wanting to keep strictly freshwater fish. On the other side of the coin, you can keep all kinds of neat brackish water fish, such as gobies, glassfish, halfbeaks, goodeids, etc., without problems.

Most aquarium plants do not like brackish water. However, at a specific gravity of 1.003, things that do well in hard water should be fine, including hornwort, Elodea, Vallisneria, Amazon swords, Bacopa, Java fern, etc.
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