Cory lathargic, need advice Pet of the Month
🐶 POTM Poll is Open! 🦎 Click here to Vote! 🐰


New Member
Jun 15, 2017
Reaction score

So I have a peppered cory who is 18 months old and a gold lazer cory.

Now, I've experienced deaths of fish over time, but my cory's became lathargic and kept swimming to the top, totally unlike them. The gold lazer cory began corkscrewing till it wouldn't move from its side. It died this morning.

I moved my peppered cory to my flatmates tank and she seems ok for now. But I've no idea why they are ill. I had a molly that was bullying the others and got rid of him yesterday, so I'm not sure if stress has made them ill.

My flatmate seems to think it's the Prime Conditioner that I'm using. He thinks it's too concentrated for a 57l tank (fluval flex).

All water parameters are fine. I've not introduced anything into the tank other than a few guppies and 2 female koi, who also look stressed thanks to the molly.

Any help or advice is appreciated
When you say Koi, do you mean Koi Carp as in coldwater fish?

57l is quite a small tank to keep fish that have been known to get up to 3ft in size. How many guppies do you have? It could be that you've just got too many fish in too small a tank.

When you say "all water parameters are fine" what exactly did you test and what are they? What temperature is the tank?
I'm glad Lunar Jetman mentioned Koi, they don't belong in a little tropical tank.

How often do you do water changes and gravel clean the substrate?

What sort of filter do you have, and how often do you clean it and how do you clean it?

When fish start spiralling through the water it is just about always caused by protozoan infections in their brain. Protozoan infections occur in tanks that have lots of organic matter in the filter and substrate, and the protozoans build up in numbers due to lack of big water changes.

If you ever lose a fish, or if the fish ever look or act funny, the first thing you should do is a 75% water change, a complete gravel clean, and clean the filter. Then see how the fish look a few hours later.
They're betta koi, not koi carp. They're now dead. Lost 3 fish this morning, 2 female guppies and one balloon molly.

I water change 20% every week, clean all filters in tank water and vacuum the gravel. All water tests came back zero and I tested ammonia, nitrite, nitrate and PH. Increased my water changes, even completing a 70% water change last week, still having deaths. Only this time there are no signs.

The fish were fine last night after a water change, swimming about with no issues so to say I was shocked they were dead today is an understatement. I've had the tank for well over a year so I'm stumped as to what is happening.

I've replaced the filter foam block and left the old one in to avoid cycling the tank. Honestly, I'm at a loss to explain this. I've left the cory in my flat mates tank and she's fine now, which frustrates me even more.
Are you using "Fish Only" buckets for water changes, or any bucket from around the house?

Can you post a picture of any of the fish?

Presumably whatever is killing them came in with the new guppies and koi bettas.
I'm not home at the moment to tske pictures. I use a fish only bucket for water changes.

I've tried everything, from removing fish i thought were bullying others, to removing ornaments that may have changed the water chemistry, to no avail. My flat mate even commented how he does quick water changes and his is fine, but i take care when cleaning my tank and fish just keep dying.
Can you post your actual test results. I would not expect nitrates or ph to be 0
PH was 7 which is fine according to my testing kit. I'll run the tests again tonight to give you exact figures but I'm almost certain nitrite and nitrates were 0
do you have any moisturising cream, oil, perfume, etc on your skin?

do you use deodorant, hair spray, air freshener, smoke, paint or do anything that produces fumes in the room?
No I don't use any of that in my room, all used in bathroom and I was my hands with normal water
Just done a water test:
Ammonia 0
Nitrite 0
Nitrate 2.5 ppm
PH 7

One of my guppys, a plain white one, is swimming at the top into the current. There's an airstone, but i know this is a sign when a guppy is on the way out. I'm still confused as to what it can be.
I cant view the images, it says I need to log in. Can you check the images to make sure you have the correct address so we can view them?
The cream guppy in the picture has very red gills and that is usually caused by water quality, gill flukes or poisoning. The water quality seems to be ok for ammonia, nitrite, nitrate & pH and gill flukes don't kill that quickly, leaving us with a possible poisoning or a protozoan infection. We should be able to rule out poisoning because you don't use anything in the room with the fish tank, and you have a flatmate that uses the same water supply and their fish are fine.

How long ago did you add the new fish (guppies & bettas)?
If it was within 2 weeks of the first fish dying then it has to be a disease. You can try using a broad spectrum medication containing Malachite Green and Formaldehyde and run that for 2 weeks and see how it goes.

Check the directions and if they don't mention anything about catfish or scaleless fish, then use it at half strength.

To work out the volume of water in the tank:
measure length x width x height in cm.
divide by 1000.
= volume in litres.

when you measure the height, measure from the top of the substrate to the top of the water level.

Because the front of the tank is curved you will have to guestimate the width of the tank. You could measure the width at the top and middle (where it bows out), and use a measurement between those two points for the width.

Before you treat the tank, wipe the inside of the glass to remove the biofilm, do a 75% water change and complete gravel clean, and clean the filter. Remove any carbon from the filter and throw that away.

Another option is to raise the water temperature to 30C and keep it there for a week. If it is a protozoan infection it will kill off the protozoans. However, if it is bacterial, fungal it will cause the disease to spread faster.

Regardless of if you try medication or heat, increase the aeration/ surface turbulence to maximise the oxygen levels in the water.

Most reactions


Members online