Cory's are dying

[Kelp23]

Hi everyone, I need some advice please. I have a 230l tank and I had 12 Cory's ( 6 pandas/6 Julii). Over the past week they've been dying for no obvious reason. I've done regular parameter checks ( ammonia 0, nitrate 0, nitrate 10, pH 7, Gh10, Kh 8). There are no signs of illness or injury. Tank mates are Hoplos, BN pleco's, 2 Bolivian rams and tetras.. any ideas what could be causing this? All other fish seem unaffected. Thanks

 

[mrsjoannh13]

How long have you had them? Are they getting enough to eat? No other symptoms before they die? Do you have sand substrate?

 

[Colin_T]

A picture tells a thousand words. Multiple pictures can tell even more. Pics of the Cories and pics of the other fishes in the tank?

How long have you had the fish?
Have you added anything to the tank in the 2 weeks before this started?

How often do you do water changes and how much do you change?
Do you have fish only buckets specifically for the fish tanks?
Has the water company done any work on the water pipes recently?
Do you dechlorinate the new water before adding it to the tank?

Do you use antibacterial soaps or have anything (moisturising cream, grease, oil, perfume, etc) on your hands when you work in the tank?

 

[Kelp23]

A picture tells a thousand words. Multiple pictures can tell even more. Pics of the Cories and pics of the other fishes in the tank?

How long have you had the fish?
Have you added anything to the tank in the 2 weeks before this started?

How often do you do water changes and how much do you change?
Do you have fish only buckets specifically for the fish tanks?
Has the water company done any work on the water pipes recently?
Do you dechlorinate the new water before adding it to the tank?

Do you use antibacterial soaps or have anything (moisturising cream, grease, oil, perfume, etc) on your hands when you work in the tank?

Hi, can't take photos right now but here is some more info:
Sand substrate no new tank mates added this year.
I've had Cory's about 12 months
Weekly water changes 60%. I drain with a Syphon and refill using a house and mixer tap. Water is matched to tank temp 25 degrees and I dose the tank with seachem prime for the full volume of the tank.
Diet is a mixture of tetra pro flakes, aqua care tropical tabs, bloodworm and fresh veggies .
I'm not aware of any water works going on and I test my tank weekly using an NT Labs kit and the parameters are the same.

I don't use creams / lotions etc on my hands

The only thing I can think of that has changed is that all my fish were originally in another tank but I bought a new one. Im wondering if the transfer process had stressed them out. The move happened about 6 weeks ago.

I can't take photos right now as I'm not home.

 

[Naughts]

Was the tank bought new or second hand?
How did you catch them? Was there a lot of chasing?
I've never heard anyone experience it but there is a myth that cories that are chased will release a toxin to deter predators. Were they kept in a bucket for a duration of time when swapping tanks?

 

[Colin_T]

Corydoras don't release toxins. They can spike each other with their pectoral fins if they are crowded and stressed but that shows up within 24 hours as red marks on the fish.

You moved the fish 6 weeks ago and this started one week ago, they have nothing to do with each other. If there was a problem with the move it would have caused problems 6 weeks ago, not now.

Whatever caused the problem happened last week. What did you do then, on the day the first one died and the day before it died?
If you did a water change on the day before or the day the first one died, the water change was most likely the problem.

 

[Kelp23]

It was a brand new tank, I part drained the original tank and removed decor to make catching them easier. All fish were places into 2 60l plastic tubs which has plants, airstone and heater. They were probably in the tub for around an hour. I've been checking water religiously as I was concerned about a spike as is transferred all the gravel into the new tank. Could my other fish be the problem? Are they getting stressed? I literally can't think of a single thing I've done differently. It's so frustrating

 

[mrsjoannh13]

It was a brand new tank, I part drained the original tank and removed decor to make catching them easier. All fish were places into 2 60l plastic tubs which has plants, airstone and heater. They were probably in the tub for around an hour. I've been checking water religiously as I was concerned about a spike as is transferred all the gravel into the new tank. Could my other fish be the problem? Are they getting stressed? I literally can't think of a single thing I've done differently. It's so frustrating

Are you using the same filter and filter media from the old tank? I moved my fish to a new tank a couple of months ago. It had a new HOB filter that came with the kit and between the stress of the move and something being wonky with the new filter I lost one fish and almost lost a second. I was using the old filter media to keep the beneficial bacteria but the new filter just wasn't cutting it. Seems like any issues would have caused the corys to die immediately or soon after the move so I'm not sure if this is a factor or not. Also, I've heard pockets of gas can get in the sand and if you don't rake the sand after you vacuum those pockets could eventually pop and release gases into the water that can be harmful. Only other thought for now.

 

[Kelp23]

Are you using the same filter and filter media from the old tank? I moved my fish to a new tank a couple of months ago. It had a new HOB filter that came with the kit and between the stress of the move and something being wonky with the new filter I lost one fish and almost lost a second. I was using the old filter media to keep the beneficial bacteria but the new filter just wasn't cutting it. Seems like any issues would have caused the corys to die immediately or soon after the move so I'm not sure if this is a factor or not. Also, I've heard pockets of gas can get in the sand and if you don't rake the sand after you vacuum those pockets could eventually pop and release gases into the water that can be harmful. Only other thought for now.

Hi, it was the same filter. I'd kept it running throughout the move. All the same media etc. I was aware of the gas thing which is why I tested quite a lot following the move in case I had an Ammonia spike. No idea what's going on. As far as I can tell I've not done anything to cause this but they don't just decide to pop off so theres something not right.

 

[mrsjoannh13]

Wow - it sounds like you are doing everything right. I'm stumped, too. I'm so sorry for your losses. Corys are awesome.

 

[Kelp23]

Thankyou. I've not lost anymore so I've got my fingers crossed for the rest.

 

[Colin_T]

Post pictures and video of all of the fish, including the Corydoras. We can check them for disease.