Corydora suddenly turned black and has a red tinted belly

Hey, so due to lockdown I’ve been left to look after my sisters fish, she has three corydoras as well as a betta and some balloon mollies. She got the corydoras a good few months ago, they seem to be very jumpy, skittish? I’m not sure what you call it when it comes to fish. But recently one turned black, pretty much over night, a lot of people were saying it’s normal on other forums, a few days in and I’ve now noticed a hint of red on its belly. I heard about something called red blotch disease, which may be the case, I’m not really sure, so I’d appreciate any help or advice. The tank has been a real pain recently, it always has been really, no matter how you clean it or how often you clean it, it never seems to get better, hence why we never have gravel, it always makes things ten times worse. I’ve been cleaning it every other day, (small water changes with one of those pump things) occasionally every day throughout the whole of lockdown, it’s never clean, I used to over feed a little but I haven’t done for the past month or so and it’s still terrible, it never seems to get better. I clean the filter and sponge most days too, I have no clue what causes it to become so dirty every single day, I’m an animal person and I have to say, fish seem to be the most high maintenance animals I have ever come across aha. I’m not much of a fish person, I don’t know how to do tests etc so any advice would be greatly appreciated. We also had the betta getting swim bladder although she seems a lot better after a few days and is almost back to normal luckily, maybe the stress of the constant cleaning is causing the issues or the dirty tank, I’m not sure, I don’t want any more ill fish so if any of you have any advice on the fish or the tank please let me know x


I’ve attached a photo of the darker corydora next to one of the others, it was the same colour just a few days ago, as well as a picture of the tank just so you can see what I mean by it’s dirty (I cleaned the sides, filter and did about a 25% water change, this is the cleanest it’s been in months) although you probably need to bare in mind that some of the sides are permanently marked as it’s an old tank. I also have a lot more ornaments and a bigger tank (honestly makes the fish act depressed in a bigger tank for some reason, maybe because a lot of the balloon mollies are very small?) but with the amount of algae I’ve only put one thing in so the betta has somewhere to hide, balloon mollies are too friendly aha, should I put some more ground ornaments down so that the corydoras have somewhere to hide as well?



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Do a 75% water change right away

The green stuff on the glass is simply algae and grows anywhere there is water and light. If you have live plants in the tank, they use the light and reduce the algae.
You don't have any live plants in the tank and algae is growing because of that.

If you don't have live plants in the tank, you only need the light on for a couple of hours in the afternoon/ evening.

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Stress from tank lights coming on when the room is dark can be an issue. Fish don't have eyelids and don't tolerate going from complete dark to bright light (or vice versa) instantly.

In the morning open the curtains or turn the room light on at least 30 minutes (or more) before turning the tank light on. This will reduce the stress on the fish and they won't go from a dark tank to a bright tank instantly.

At night turn the room light on and then turn the tank light off. Wait at least 30 minutes (or more) before turning the room light out. This allows the fish to settle down for the night instead of going from a brightly lit tank to complete darkness instantly.

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How do you clean the filter?

I think , bottom line that it's over populated tank. No plants , too many fish. Try the big water changes but I can't see it ever working. This tank seems bad in so many ways so time to start again for the sake of the fish. I'll explain if needed,

Add some gravel to the floor to start, add plants even if plastic for height and cover. 50% water change per week. Limit feeding until the fish boil at your sight as I think over feeding is an issue. Then I think you will have a more enjoyable time.

Colin_T said:

The green stuff on the glass is simply algae and grows anywhere there is water and light. If you have live plants in the tank, they use the light and reduce the algae.
You don't have any live plants in the tank and algae is growing because of that.

If you don't have live plants in the tank, you only need the light on for a couple of hours in the afternoon/ evening.

---------
Stress from tank lights coming on when the room is dark can be an issue. Fish don't have eyelids and don't tolerate going from complete dark to bright light (or vice versa) instantly.

In the morning open the curtains or turn the room light on at least 30 minutes (or more) before turning the tank light on. This will reduce the stress on the fish and they won't go from a dark tank to a bright tank instantly.

At night turn the room light on and then turn the tank light off. Wait at least 30 minutes (or more) before turning the room light out. This allows the fish to settle down for the night instead of going from a brightly lit tank to complete darkness instantly.

---------------
How do you clean the filter?

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Ah Thankyou, never been sure of how long to leave the light on for. I normally take it apart fully and clean it in the water from a water change.

Guppy10 said:

I think , bottom line that it's over populated tank. No plants , too many fish. Try the big water changes but I can't see it ever working. This tank seems bad in so many ways so time to start again for the sake of the fish. I'll explain if needed,

Click to expand...

I can do as I do have a bigger tank, I used to have all of the balloon mollies in there (they were all unexpected as the ones my sister bought were pregnant) but they’ve never seemed to be comfortable in it, they constantly were hiding, not moving really and not really eating. In the smaller tank they seem happier? I’m not really sure, the corydoras don’t seem happy in the smaller tank at all though. I’m not sure what to do as I don’t want to put them in such a big tank, I know a lot of animals can get overwhelmed by big sized cages, is it the same with some fish?

Guppy10 said:

Add some gravel to the floor to start, add plants even if plastic for height and cover. 50% water change per week. Limit feeding until the fish boil at your sight as I think over feeding is an issue. Then I think you will have a more enjoyable time.

Click to expand...

Thankyou, I’ll definitely do that

Lucy Corbettt said:

Hey, so due to lockdown I’ve been left to look after my sisters fish, she has three corydoras as well as a betta and some balloon mollies. She got the corydoras a good few months ago, they seem to be very jumpy, skittish? I’m not sure what you call it when it comes to fish. But recently one turned black, pretty much over night, a lot of people were saying it’s normal on other forums, a few days in and I’ve now noticed a hint of red on its belly. I heard about something called red blotch disease, which may be the case, I’m not really sure, so I’d appreciate any help or advice. The tank has been a real pain recently, it always has been really, no matter how you clean it or how often you clean it, it never seems to get better, hence why we never have gravel, it always makes things ten times worse. I’ve been cleaning it every other day, (small water changes with one of those pump things) occasionally every day throughout the whole of lockdown, it’s never clean, I used to over feed a little but I haven’t done for the past month or so and it’s still terrible, it never seems to get better. I clean the filter and sponge most days too, I have no clue what causes it to become so dirty every single day, I’m an animal person and I have to say, fish seem to be the most high maintenance animals I have ever come across aha. I’m not much of a fish person, I don’t know how to do tests etc so any advice would be greatly appreciated. We also had the betta getting swim bladder although she seems a lot better after a few days and is almost back to normal luckily, maybe the stress of the constant cleaning is causing the issues or the dirty tank, I’m not sure, I don’t want any more ill fish so if any of you have any advice on the fish or the tank please let me know x


I’ve attached a photo of the darker corydora next to one of the others, it was the same colour just a few days ago, as well as a picture of the tank just so you can see what I mean by it’s dirty (I cleaned the sides, filter and did about a 25% water change, this is the cleanest it’s been in months) although you probably need to bare in mind that some of the sides are permanently marked as it’s an old tank. I also have a lot more ornaments and a bigger tank (honestly makes the fish act depressed in a bigger tank for some reason, maybe because a lot of the balloon mollies are very small?) but with the amount of algae I’ve only put one thing in so the betta has somewhere to hide, balloon mollies are too friendly aha, should I put some more ground ornaments down so that the corydoras have somewhere to hide as well?



iView attachment 102297View attachment 102298

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So, I did a 75% water change and added some gravel and some more ornaments, it’s looking a lot better I’m just hoping that the gravel doesn’t cause too many problems. I still don’t know what’s up with the Cory Dora but I’m hoping having more places to hide will help. Thankyou all for the advice

Get a basic model gravel cleaner like the one in the following link. Use it to clean the substrate without removing the substrate.

If you can't afford a gravel cleaner, you can make one out of a 1, 1.5 or 2 litre plastic drink bottle and a length of plastic hose or garden hose.
Cut the bottom off the bottle and throw the bottom bit away.
Remove the cap and plastic ring from the top of the bottle and throw those 2 bits away.
Put a length of garden hose in the top of the bottle and the other end of the garden hose in a bucket or roll it out onto the lawn.
Use the bottle as the gravel cleaner to clean and drain some water out of the tank.

There's a number of videos on YouTube showing how to use a gravel cleaner.

Colin_T said:

Get a basic model gravel cleaner like the one in the following link. Use it to clean the substrate without removing the substrate.

Aquarium Cleaning Made Easy

Aquarium cleaning should take 30 minutes every two weeks. Learn how the professionals do it in 18 easy steps.

www.about-goldfish.com

If you can't afford a gravel cleaner, you can make one out of a 1, 1.5 or 2 litre plastic drink bottle and a length of plastic hose or garden hose.
Cut the bottom off the bottle and throw the bottom bit away.
Remove the cap and plastic ring from the top of the bottle and throw those 2 bits away.
Put a length of garden hose in the top of the bottle and the other end of the garden hose in a bucket or roll it out onto the lawn.
Use the bottle as the gravel cleaner to clean and drain some water out of the tank.

There's a number of videos on YouTube showing how to use a gravel cleaner.

Click to expand...

I do actually have one but it’s a bit smaller then the one in the link. As far as I know gravel has always caused my sister problems but maybe that was because she was over feeding them, hopefully this time it should all be okay. Thankyou for the advice

A smaller gravel cleaner is fine. Just use it every time you do a water change and the gravel will stay clean and the fish will be happy.

Lucy Corbettt said:

I can do as I do have a bigger tank, I used to have all of the balloon mollies in there (they were all unexpected as the ones my sister bought were pregnant) but they’ve never seemed to be comfortable in it, they constantly were hiding, not moving really and not really eating. In the smaller tank they seem happier? I’m not really sure, the corydoras don’t seem happy in the smaller tank at all though. I’m not sure what to do as I don’t want to put them in such a big tank, I know a lot of animals can get overwhelmed by big sized cages, is it the same with some fish

Click to expand...

No, the more space they have to swim, the better. It also makes it healthier because the quality of smaller water volumes can be poor. However any tank should be cycled meaning beneficial bacteria are on the surfaces (gravel, filter sponge etc.) So I would guess that your bigger tank is not cycled which is why the fish were not happy. Read up on cycling in the beginners section and get the big tank cycled (this can take 2-8 weeks).
The other problem is the Betta is not a community fish and should be in its own. Here the Betta and the other fish will be stressed. Once you have the big tank cycled, move the cories and mollies over leaving the Betts on its own.
Ask if you have questions.

Naughts said:

No, the more space they have to swim, the better. It also makes it healthier because the quality of smaller water volumes can be poor. However any tank should be cycled meaning beneficial bacteria are on the surfaces (gravel, filter sponge etc.) So I would guess that your bigger tank is not cycled which is why the fish were not happy. Read up on cycling in the beginners section and get the big tank cycled (this can take 2-8 weeks).
The other problem is the Betta is not a community fish and should be in its own. Here the Betta and the other fish will be stressed. Once you have the big tank cycled, move the cories and mollies over leaving the Betts on its own.
Ask if you have questions.

Click to expand...

We had the big tank cycled for over a month before we put the fish in, but they still didn’t seem happy in it. May try again with it soon though. The betta we have actually gets along really well with the other fish, it never has stress lines on it and due to it being female, it really isn’t violent towards the other fish at all. Thankyou for the advice I’ll most likely cycle the big tank again and maybe move the balloon mollies in there after a month or so

Did you add ammonia to cycle the tank? A lot of people just leave the tank to run, not realising that this is not cycling.