Molly fish holding in top fin and sitting at the bottom of the tank a lot

JWKelly99

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Hi all,

I've recently got 2 molly fish - I've had them about 2 weeks - and one of them has started tucking in its fins and sitting at the bottom of the tank a lot. I've tried upping the temperature in the tank (its sat at 80*f) and have done 2 water changes since I got them. I'm currently waiting on an ammonia test kit (due to come tomorrow) so that I can make sure the ammonia and nitrates are at 0. I'm not sure what's wrong with my fish though. One of them recently had 5 babies (I think it was the other one) but that seems to be all that's changed in the tank since I got them. Does anybody have any advice or ideas I could try to see what is wrong with the fish? I've been reading around and it suggested doing a 10% water change everyday for a week to try and sort the water conditions out. For reference, I've got a biorb 15l tank.

thank you in advance for your help.
 
What else is in the tank with them? 15 litres is far too small a tank for mollies I'm afraid. Not many fish can live in 15 litres of water, and mollies get large. You're also very quickly going to have bad water conditions when they're having fry in there too. Any other fish?
 
What else is in the tank with them? 15 litres is far too small a tank for mollies I'm afraid. Not many fish can live in 15 litres of water, and mollies get large. You're also very quickly going to have bad water conditions when they're having fry in there too. Any other fish?
There's no other fish in the tank with them. The people at Pets at Home said that 2 mollies would be fine in our tank because the tank is 8 fish points and mollies are only 3 each. I don't know if that's a Pets at Home thing or if that's used more widely? We also have some fake plant in there with them for the fry to hide in but that's all. Is there anything we could do to help them in the tank?
 
There's no other fish in the tank with them. The people at Pets at Home said that 2 mollies would be fine in our tank because the tank is 8 fish points and mollies are only 3 each. I don't know if that's a Pets at Home thing or if that's used more widely? We also have some fake plant in there with them for the fry to hide in but that's all. Is there anything we could do to help them in the tank?
I'm sorry, I completely understand when you're new to the hobby that it makes sense to trust the advice of fish stores, especially a big chain. Iogically, they should know what they're talking about, and give sound advice, so it's not your fault you believed them. But the hard lesson a lot of people only learn when their fish start dying is that fish store advice is terrible advice, especially from the big chains.

Fish keeping is too complex to break down into a points system. That's a pets at home thing, they try that to create some kind of basic standard across stores, but it doesn't work, and at the end of the day, animal welfare laws are rarely applied to fish, and the store is there to make money, even if it means selling you a tiny tank and fish that can't live in it. Many of the employees will have never kept a tank, wouldn't have the time to explain what the nitrogen cycle is if they even know, and need to sell you fish and fish accessories. They place some limits, but not nearly enough since it wouldn't be good for business.

But do some research on mollies. Look at how large they get. I don't know which species of molly you have, but your average black molly female can reach 12 cms in length. Measure out 12 cms, then measure how wide your tank is. Your tank is less than five gallons of water, and has very little horizontal swimming space. So size alone, bearing in mind that mollies keep growing and yours might be old enough to reproduce, but likely aren't fully grown maximum size yet since you just bought them... they're going to outgrow your tank if they haven't already.

I'll give you an example from my father's tank for scale. See that yellow fish on the left? and the black fish right abve it, about the same size? That's an adult yellow molly, and an adult black molly. Probably about the same size as yours are now, roughly. The much larger black and silver dappled fish below the yellow one? That's a fully grown adult black molly. They can get BIG. This tank is 57 gallons, yours is less than five. That fully grown adult molly would be so cramped in there, and you need to consider the whole lifespan of the fish, and how active they are when they swim. Mollies are strong swimmers, and active fish, on the move all day. They need space for that.
DSCF1662.JPG


Seriously Fish is a trusted resource, written by scientists about fish care requirements for different species, have a look at the information about mollies here, especially the minimum tank size.

The other aspect of a small tank is that it's very hard to maintain suitable water conditions. Did the store explain tank cycling to you? I'll link a video, but in a nutshell, fish eat/breathe etc, they excrete ammonia. Leftover food or rotting plant material turns into ammonia. Ammonia is very toxic to fish. In the wild this isn't a problem since the waste is diluted in huge volumes of water and bacteria break it down, but in a small enclosed ecosystem like a tank, it can become a big problem, very fast. Ammonia burns fish, it burns their gills, their skin, damages them internally if they're forced to swim in it. We have filters mainly for this reason, to grow the kind of bacteria that converts ammonia into less toxic compounds, making the water safe for the fish. Cycling a tank properly takes weeks, usually longer than a month, but pets at home tells people to set up a tank, wait a week, then add fish. This does nothing to actually cycle the tank, and leads to a lot of fish deaths. I'm hoping that since you're here, it won't happen to you, now you have a chance t learn how to cycle the tank and make sure it's safe. Do you have a water testing kit?

That's a really simplified explanation but it's late and this reply is already super long, I'm sorry! This video gives a really clear explanation of what the nitrogen cycle is, and why it's so important in fish keeping.

So your two mollies will be producing ammonia. In a 15 litre tank, even a small amount of ammonia is very risky, since there's so little water to dilute it. It would take two fish a long time to produce enough ammonia to make the levels toxic in a 200 litre tank, but a 15 litre tank is going to reach toxic levels much more rapidly, as an example. So you'd need to do very regular water changes for the water to be safe for them, even once the tank is cycled.

Sorry, that's a lot of info to dump on you, and I don't know how much of it you might already know. For now, you can help the fish by doing large daily water changes. It's likely that the fish is clamping its fins and sitting on the bottom because ammonia and/or nitrites are too high, and it's stressed and feeling the toxic effects. If you change 75% of the water, making sure to use a water conditioner and temperature match the new water to the tank water before adding it in to the tank, it should help the fish get by until tomorrow. Do those daily for now, while we see where you're at in the cycle.

In the long term, a larger tank, or different fish will be needed. But for now, large daily water changes are the best thing you can do for them. Also be careful not to over feed them. Too much food means more ammonia.
Sorry for the essay, will try to check in again tomorrow!
 
I'm sorry, I completely understand when you're new to the hobby that it makes sense to trust the advice of fish stores, especially a big chain. Iogically, they should know what they're talking about, and give sound advice, so it's not your fault you believed them. But the hard lesson a lot of people only learn when their fish start dying is that fish store advice is terrible advice, especially from the big chains.

Fish keeping is too complex to break down into a points system. That's a pets at home thing, they try that to create some kind of basic standard across stores, but it doesn't work, and at the end of the day, animal welfare laws are rarely applied to fish, and the store is there to make money, even if it means selling you a tiny tank and fish that can't live in it. Many of the employees will have never kept a tank, wouldn't have the time to explain what the nitrogen cycle is if they even know, and need to sell you fish and fish accessories. They place some limits, but not nearly enough since it wouldn't be good for business.

But do some research on mollies. Look at how large they get. I don't know which species of molly you have, but your average black molly female can reach 12 cms in length. Measure out 12 cms, then measure how wide your tank is. Your tank is less than five gallons of water, and has very little horizontal swimming space. So size alone, bearing in mind that mollies keep growing and yours might be old enough to reproduce, but likely aren't fully grown maximum size yet since you just bought them... they're going to outgrow your tank if they haven't already.

I'll give you an example from my father's tank for scale. See that yellow fish on the left? and the black fish right abve it, about the same size? That's an adult yellow molly, and an adult black molly. Probably about the same size as yours are now, roughly. The much larger black and silver dappled fish below the yellow one? That's a fully grown adult black molly. They can get BIG. This tank is 57 gallons, yours is less than five. That fully grown adult molly would be so cramped in there, and you need to consider the whole lifespan of the fish, and how active they are when they swim. Mollies are strong swimmers, and active fish, on the move all day. They need space for that.
View attachment 116117

Seriously Fish is a trusted resource, written by scientists about fish care requirements for different species, have a look at the information about mollies here, especially the minimum tank size.

The other aspect of a small tank is that it's very hard to maintain suitable water conditions. Did the store explain tank cycling to you? I'll link a video, but in a nutshell, fish eat/breathe etc, they excrete ammonia. Leftover food or rotting plant material turns into ammonia. Ammonia is very toxic to fish. In the wild this isn't a problem since the waste is diluted in huge volumes of water and bacteria break it down, but in a small enclosed ecosystem like a tank, it can become a big problem, very fast. Ammonia burns fish, it burns their gills, their skin, damages them internally if they're forced to swim in it. We have filters mainly for this reason, to grow the kind of bacteria that converts ammonia into less toxic compounds, making the water safe for the fish. Cycling a tank properly takes weeks, usually longer than a month, but pets at home tells people to set up a tank, wait a week, then add fish. This does nothing to actually cycle the tank, and leads to a lot of fish deaths. I'm hoping that since you're here, it won't happen to you, now you have a chance t learn how to cycle the tank and make sure it's safe. Do you have a water testing kit?

That's a really simplified explanation but it's late and this reply is already super long, I'm sorry! This video gives a really clear explanation of what the nitrogen cycle is, and why it's so important in fish keeping.

So your two mollies will be producing ammonia. In a 15 litre tank, even a small amount of ammonia is very risky, since there's so little water to dilute it. It would take two fish a long time to produce enough ammonia to make the levels toxic in a 200 litre tank, but a 15 litre tank is going to reach toxic levels much more rapidly, as an example. So you'd need to do very regular water changes for the water to be safe for them, even once the tank is cycled.

Sorry, that's a lot of info to dump on you, and I don't know how much of it you might already know. For now, you can help the fish by doing large daily water changes. It's likely that the fish is clamping its fins and sitting on the bottom because ammonia and/or nitrites are too high, and it's stressed and feeling the toxic effects. If you change 75% of the water, making sure to use a water conditioner and temperature match the new water to the tank water before adding it in to the tank, it should help the fish get by until tomorrow. Do those daily for now, while we see where you're at in the cycle.

In the long term, a larger tank, or different fish will be needed. But for now, large daily water changes are the best thing you can do for them. Also, be careful not to overfeed them. Too much food means more ammonia.
Sorry for the essay, will try to check in again tomorrow!
Thank you for all that. It's very useful. I've done another large water change today and am planning on promoting the bacteria for the time being with the filter boost I've got. I wasn't aware of cleaning the filter with the tank water so I did it with tap water a few days ago. So now I've started the filter boost cycle from fresh again to restore the bacteria to help keep the ammonia and such down. Do you know how long it'll take for the nitrogen cycle to start working? Also, how long after the tank conditions improve will it take for the fish to stop having clamped fins?
 
I forgot to mention that the fish seems to be getting a little better. Its no longer sitting on the bottom of the tank and is swimming around again. Its also spreading its back fin more than yesterday so I'm thinking this is a good sign?
 
Thank you for all that. It's very useful. I've done another large water change today and am planning on promoting the bacteria for the time being with the filter boost I've got. I wasn't aware of cleaning the filter with the tank water so I did it with tap water a few days ago. So now I've started the filter boost cycle from fresh again to restore the bacteria to help keep the ammonia and such down. Do you know how long it'll take for the nitrogen cycle to start working? Also, how long after the tank conditions improve will it take for the fish to stop having clamped fins?
I forgot to mention that the fish seems to be getting a little better. Its no longer sitting on the bottom of the tank and is swimming around again. Its also spreading its back fin more than yesterday so I'm thinking this is a good sign?
You're not the first nor the last to rinse filter media in tank water, so you're in good company, it happens :) Fortunately the bacteria live on every hard surface in the tank, in the substrate, tank walls, on decor, so hopefully there will be enough bacteria to help re-build the colony quickly. Some of the bacteria deep in the filter might have survived too, so chances are you're not starting over from the beginning, but the colony will need a week or so to regrow enough to handle the bioload of the tank. When something like this happens, we call it a mini-cycle, since you're unlikely to have wiped out all of the bacteria, but they still need time to rebuild to a good size.

Best to do 75% water changes daily for now, to make sure ammonia and nitrites stay at zero. Invest in a decent water testing kit, the API freshwater master test kit is the one most hobbyists rely on. The liquid kits like API or NT labs are more accurate than dip strips, which is important when something goes wrong. Test the water daily, and do a large water change anytime ammonia or nitrites are above zero, or when nitrates get to 20ppm or above. Once ammonia and nitrites are staying at zero again, then the tank is cycled. It usually takes about a week of large daily water changes to keep the water safe, for the bacteria to rebuild.

It's great that the molly is swimming around again and no longer fin clamped! That's because the water change dropped the ammonia and nitrite levels, so she isn't so stressed. :) Keep on top of those water changes and testing, and they should be okay!

Try not to overfeed them while the cycle is re-establishing. More food means more ammonia. It's trickier since you have young fry who need to eat frequently, while the adults could easily go for a few days without being fed. Keep the meals small. Finely crush the flake, try to make sure the fry get some, but drop in a little at a time, and no more than they can eat in two minutes. If food is hitting the substrate, you're feeding too much at once. Gravel vac the substrate when you do a water change to remove as much uneaten food and fish poop as possible.

In the meantime, if you can get hold of some fast growing live plants, like floating plants, and/or big bunches of elodea, hornwort, water wisteria - something like that, those plants grow quickly, and suck up ammonia before it gets turned into nitrites and then nitrates. They can really help with water quality, and the fish like them too.

In the longer term, a larger tank is going to be essential to keep mollies, especially if you're raising fry too. How many fry do you have now? For mollies, I wouldn't go smaller than a 100 litre tank, especially when they're producing fry. Fry need feeding often, produce a lot of waste, and grow fast - overcrowding tanks pretty quickly. And bear in mind that female mollies can store sperm for a year or more and keep having fry even without a male around. Each female can drop 30-40 fry (average) each month. It's a lot of fish.

If you can't go larger, you'll probably need to return the mollies I'd afraid. People here can suggest smaller species that might be okay in a 15 litre biorb, but your options would be really limited.
 
I've just had some dip strips arrive for the meantime until I can get a better testing kit. Unfortunately, it's only an ammonia one which says the ammonia is at about 1ppm. Should I do another water change today or leave it till tomorrow as to not stress the fish to much?

I've got 5 fry at the minute, but once they get a bit bigger I'm planning on returning them to Pets at Home as I obviously can't keep them in my tank. Is there anything I can do to keep the mollies in this tank as I don't have the money for a new tank and also don't really want to return them as they were a gift for my girlfriend?

Thank you for the tips regarding feeding them. It's still holding its top fin in a bit, but the back fin seems to be a lot more spread than it was yesterday and its swimming around like normal the majority of the time
 
I've just had some dip strips arrive for the meantime until I can get a better testing kit. Unfortunately, it's only an ammonia one which says the ammonia is at about 1ppm. Should I do another water change today or leave it till tomorrow as to not stress the fish to much?

I've got 5 fry at the minute, but once they get a bit bigger I'm planning on returning them to Pets at Home as I obviously can't keep them in my tank. Is there anything I can do to keep the mollies in this tank as I don't have the money for a new tank and also don't really want to return them as they were a gift for my girlfriend?

Thank you for the tips regarding feeding them. It's still holding its top fin in a bit, but the back fin seems to be a lot more spread than it was yesterday and its swimming around like normal the majority of the time
Do the water change ASAP. Ammonia levels are far more stressful for fish than water changes are, ammonia can kill them, water changes are a minor annoyance at best.

I don't think Pets At Home are willing to accept livebearer fry from hobbyists at home, because of the risk of the spread of diseases. You'd need to contact them to double check, but they usually won't.

Check places like gumtree for second hand tanks. You can get some bargains, and many will include a heater, filter, lights etc. I wouldn't keep them the biorb for life, no. Even if it means saving up for a second hand tank and not getting one that's as 'pretty' or 'cute' as a biorb. Fish welfare trumps decor choices, since these are living beings we're talking about. Fish that are kept in too small tanks have stunted growth. Some people don't see that as a problem, "the fish grows to the size of the tank" is an old myth. But the internal organs continue to grow, and even when the body is stunted, this damages the fish and they die young.

Not to mention that within three months, you'll have seven adult mollies in there, all capable of breeding and producing even more...
 
Just read through all this and wanted to reassure you that you're not failing at this or doing a bad job, I myself didn't do enough research and got bad advice from a LFS who basically fed me a load of BS, I ended up doing a fish in cycle. It wasn't the best way to start but it sure taught me so much about the scientific side.
Also, the Pets at Home thing, I've been in two branches locally and have to admit, I was very impressed ear-wigging conversations with customers. I don't agree with the points thing i.e. they sell Clown Loaches - they grow massively long in comparison to your standard box shop tank - it just contradicts the tanks they offer I guess.
I would change 50-70% water every single time ammonia or nitrite are even 0.25. In my own fish in cycle I sometimes ended up doing 2 water changes a day.
Good luck! You'll get used to the way a healthy fish acts compared to random or different acts, such as sitting at the top of bottom, not moving, fin problems etc. They will become far more obvious when your tank is cycled and in good stead.
 

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