Mollie Strange Behaviour

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Aquarium Advice Newbie
Sep 30, 2022
I was wondering if anyone could help with this please.

I bought 3 mollies on the 24th September 2 female's and a male. Female's seem fine and very active. Male spends most of his time at the bottom of the tank, will swim a few inches up occasionally but tends to move around the bottom and settle in one place for an hour at a time. Seems quite alert and is feeding.

Amonia 0,nitrites 0,nitrate 20, ph 7.2 -.7.5, temp 26°C testing every 2-3 days and remains stable. 2 x 30% water changes a week apart,water treated with Fluval conditioner.

They are in a 105 litre tank,fishless cycle for a month and no other fish in the tank.

Filter is a Asap 700 and i also bought an airstone a few days ago.

Acclimatised the fish by leaving the bag floating on the tank for 30 minutes and then adding in tank water. Fish bought locally.

Tank has sand substrate and has been cleaning every few days with a net, also contains driftwood,stones and plants java fern, hornswort, moss ball and anubis.

Last water change was yesterday.

Has been fed tropical fish flakes and tetra micro crisps and algae wafer.

I purchased some swim bladder treatment and have dosed it every 48 hours at required amount for the past 6 days. His swimming looks okay but just been trying to rule it out. Also i didn't feed him for 2 days early on to see if that would help.

Behaviour hasn't changed and I'm at a loss at what to do next,any help would be greatly appreciated. Thank you


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Make sure too add a little marine salt too there water they are also a brackish fish our mollies love the specific gravity at about 1.006 that should help there behavior out
Hi and welcome to the forum :)

What is the GH (general hardness) and KH (carbonate hardness) of your water supply?
This information can usually be obtained from your water supply company's website or by telephoning them. If they can't help you, take a glass full of tap water to the local pet shop and get them to test it for you. Write the results down (in numbers) when they do the tests. And ask them what the results are in (eg: ppm, dGH, or something else).

Mollies need a GH above 250ppm and a pH above 7.0. Your pH is fine but the GH might be too low.

There are no cures for swim bladder problems and true swim bladder problems are uncommon. So no more swim bladder treatments please.

If a fish floats up when it stops swimming, it might have a swim bladder issue or it might have air trapped in its intestine. To test this you stop feeding dry food for a week and feed frozen or live foods instead. If the problem stops after you remove dry food form the diet, then the issue was air in the fish's intestine.

If a fish sinks to the bottom when it stops swimming, then it has a swim bladder issue. There is no cure for this.

Sinking to the bottom is different from a fish swimming level or hovering around the bottom. Fish that don't feel well will sometimes sit on the bottom or hang out near the bottom of the aquarium, or up at the surface near a filter outlet gasping.


The fish in the picture looks skinny and could have worms and or gill flukes.

What does the fish's poop look like?
Is the fish still eating well?

You can normally treat gill flukes with salt, see directions below.
Intestinal worms can be treated with Flubendazole or Praziquantel for tapeworms, and Levamisole for thread/ round worms. I will post the deworming info below.

I would use salt first and if there's no improvement after a week with salt, maybe try treating the fish for thread worms.


You can add rock salt (often sold as aquarium salt), sea salt, or swimming pool salt to the aquarium at the dose rate of 1 heaped tablespoon per 20 litres of water. If there is no improvement after 48 hours you can double that dose rate so there is 2 heaped tablespoons of salt per 20 litres.

If you only have livebearers (guppies, platies, swordtails, mollies), goldfish or rainbowfish in the tank you can double that dose rate, so you would add 2 heaped tablespoons per 20 litres and if there is no improvement after 48 hours, then increase it so there is a total of 4 heaped tablespoons of salt per 20 litres.

Keep the salt level like this for at least 2 weeks but no longer than 4 weeks otherwise kidney damage can occur. Kidney damage is more likely to occur in fish from soft water (tetras, Corydoras, angelfish, Bettas & gouramis, loaches) that are exposed to high levels of salt for an extended period of time, and is not an issue with livebearers, rainbowfish or other salt tolerant species.

The salt will not affect the beneficial filter bacteria but the higher dose rate (4 heaped tablespoons per 20 litres) will affect some plants and some snails. The lower dose rate (1-2 heaped tablespoons per 20 litres) will not affect fish, plants, shrimp or snails.

After you use salt and the fish have recovered, you do a 10% water change each day for a week using only fresh water that has been dechlorinated. Then do a 20% water change each day for a week. Then you can do bigger water changes after that. This dilutes the salt out of the tank slowly so it doesn't harm the fish.

If you do water changes while using salt, you need to treat the new water with salt before adding it to the tank. This will keep the salt level stable in the tank and minimise stress on the fish.

When you first add salt, add the salt to a small bucket of tank water and dissolve the salt. Then slowly pour the salt water into the tank near the filter outlet. Add the salt over a couple of minutes.

Intestinal Worms like tapeworm and threadworms cause the fish to lose weight, continue eating and swimming normally, and usually do a stringy white poop. Fish can do this for months and not be too badly affected. In some cases, fish with a bad worm infestation will actually gain weight and get fat and look like a pregnant guppy. This is due to the huge number of worms inside the fish.

Livebearers like guppies, mollies, swordtails & platies are regularly infected with gill flukes and intestinal worms. If the fish are still eating well, then worms is the most likely cause of weight loss.

You can use Praziquantel to treat tapeworm and gill flukes. And use Levamisole to treat thread/ round worms. If you can't find these medications, look for Flubendazole, which treats both lots of worms.

In the UK look for:
eSHa gdex contains praziquantel that treats tapeworm and gill flukes.
eSHa-ndx contains levamisole and treats thread/ round worms.
NT Labs Anti-fluke and Wormer contains flubendazole.
Kusuri wormer plus (contains flubendazole) - sold mainly for discus, comes as a powder which is quite hard to dose in smaller tanks
Sera nematol (contains emamectin)

Remove carbon from filters before treatment and increase aeration/ surface turbulence to maximise oxygen levels in the water.

You treat the fish once a week for 4 weeks. The first treatment will kill any worms in the fish. The second, third and forth treatments kill any baby worms that hatch from eggs inside the fish's digestive tract.

Treat every fish tank in the house at the same time to prevent cross contamination.

You do a 75% water change and complete gravel clean 24-48 hours after treatment. Clean the filter 24 hours after treatment too.

Do not use the 2 medications together. If you want to treat both medications in a short space of time, use Praziquantel on day one. Do a 75% water change and gravel clean the substrate on day 2 & 3. Treat the tank with Levamisole on day 4 and do a 75% water change and gravel clean on day 5, 6 & 7 and then start with Praziquantel again on day 8.

The water changes will remove most of the medication so you don't overdose the fish the next time you treat them. The gravel cleaning will suck out any worms and eggs that have been expelled by the fish. Repeating the treatment for 3-4 doses at weekly intervals will kill any worms that hatch from eggs. At the end of the treatment you will have healthier fish. :)
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