Corydoras Dying.

[TheRandomHero]

Hey everyone.
 
Long story short: I set up my tank (gravel sub, unplanted, 40L) successfully fishless cycled it, and stocked with 5 HQ Rasboras and 3 Peppered Corys about 3-4 weeks ago. 4 days ago the smallest of the Corys was floating to the top, a gentle tap on the glass made him swin down, only to float straight back up.
 
Google revealed a possible swim bladder infection, which apparently is extremely rare to survive. I did a 50% WC (I've ben doing a 35% every 4-5 Days since I got the tank, we live in a high nitrates area) hoping it would help. The next morning he was dead at the bottom of the tank, and I just thought it an unfortunate one off...
 
Friday night I noticed one of the others showing the same symtoms, but the Aquarium store was closed and will be until tuesday. Sure enough the next day he was also dead
 
Now my final cory is showing slight symptoms, and even though he isnt floating he isn't level when resting on the gravel, he sort of leans to the side.
 
Over the last few days, since after the 1st Cory died, the water in the tank has looked a little cloudy. Tests revealed 0.25 Ammonia and 0.25 Nitrites on Friday night, and 0.25 / 0.0 this morning, so they're not alarmingly high or spiking. I don't overfeed, I feed a small pinch of bloodworms every 2 days, and a small algae pellet for the cory's also every 2 days.
 
I can't possibly think what could be wrong but the HQ Rasboras seem just fine. No signs of stress, eating normally, swimming in their usual area....
 
Any help would be greatly appreciated as I'm at a loose end on this one


Another thing to note, the temperature is a solid 27'C, and the tank is far from windows so can never be in direct sunlight, I have the aquarium lamp on for about 4-5 hours a day, usually late afternoon til 7/8...

 

[Mikey1]

bloodworms and algae pellets are not very nutritious, and will not provide a well balanced diet for your fish....start using a good quality flake food as their staple diet....use the blood worms and pellets sparingly, once or twice a week....
 
i think you have added too many fish too quickly....a newly cycled aquarium should only see 2-3 new fish every two weeks....

 

[Lilfishy]

Your ammonia & nirites should be zero if your tank is fully cycled.
I'd do a large water change & test your water again to get it down
27 degrees is too high for peppered corys they prefer cooler temperatures around 22 degrees, also imo peppers need a larger tank as they can grow to almost 3"

 

[snazy]

There's ammonia and nitrIte in the water,  so that's the reason. You need to do large water changes to bring these down to 0 and keep it like that until the filter starts coping with the bioload.

 

[TheRandomHero]

I figured the slight ammonia and nitrite was from a small spike, as obviously even though it is cycled it still needs to adjust to the fish's bioload. I do use flakes but I stopped because the Rasboras don't eat them and cory's usually leave them on the bottom.... So I thought I better stop using them as it'll just end up polluting the water....

 

[snazy]

If the fish don't eat them, don't feed these flakes at all. Feed different food and not that much to cause left overs, or remove the left overs.
Yes, the tank hasn't adjusted yet, but fish are sensitive to these spikes and if they don't kill them on their own, they'll bring out a disease outbreak. Do a large water change with dehclorinated and temperature matched water. Test the tank, if ammonia and nitrIte aren't measuring 0 yet, do another one until it does. Then test regularly and do a water change immediately if you measure anything.
This way, fish will make it and you are giving a chance to the affected ones to recover. Some fish are more sensitive, some fish exhibit different symptoms.

 

[george4593]

Not sure if this has been mentioned. but i think I'm right in saying this? it could be because of the gravel (im not a fish expert) but ive sort of had the same problem because there barbs they use to find the food with get worn down on the gravel and could cause them to not feed

 

[mark4785]

A fine sand is the best substrate for Corydoras. I'm not sure of the suitability of gravel with it being so jagged which will cause a lot of friction on the barbels.
 
The ammonia/nitrite reading is too high. These high readings will be preventing the fish from taking up o2 by damaging the gills and preventing haemoglobin from being produced in the blood. They will also be irritating the swim bladder organ  which ultimately causes problems with buoyancy.
 
My recommendation would be to do:
- a 100% water change.
- Acclimatise your fish to a temporary holding tank of the same water temperature.
- Be sure to fully dechlorinate the replacement water and add it to the main aquarium (use twice as much dechlorinator if it is safe to do so).  
- Put the fish back into the main aquarium.
- Feed the fish sparingly once a day.
- If the fish shows sign of illness, correct the inappropriate ammonia and nitrite levels before adding any medication.

 

[This Old Spouse]

I see a lot of possibilities, and I think they've all been named above. I don't think your tank was fully cycled, and the ammonia and nitrite likely did them in.
 
A fully cycled tank done using the fishless cycle should be fine to add a full load of fish.
 
The gravel is a bad idea, but it wouldn't kill the fish in so short a time. 
 
So sorry for the loss. I hate losing cory most of all. I just lost a bronze yesterday, but I think it was old age. 

 

[TheRandomHero]

Well I did daily changes and the rest of the fish seem fine and the tank seems to have cleared up too... I am just confused because i didnt think a ammonia/nitire spike would cause visibly different water... however it does seem a mini cycle or spike was the cause... even though the tank was fully cycled maybe adding 5 Harlequins into a 40l at once disrupted the balance, because the 3 Cory's were happy for a couple of weeks before i added the HQ's.
 
regardless everything is 0 again and the remaining cory seems happy. I'll have to get him a couple of tank mates because atm he is all alone

 

[snazy]

40L is a small tank so probably you are right, adding 5 fish at once can cause a mini spike and the weaker fish can be affected.
Another possibility could be that they were already sick and it took 2 weeks for them to die, the spike being the culprit. Corys can hang on for a long time when sick unfortunately as they are hard enough this way. It's hard to figure what's wrong sometimes and it's horrible when it happens.
It's always best to add a group of fish at once, so if you take that road in the future. Do 50% water changes daily for a week to help the bacteria catch up.

 

[wko70]

I also had problems with corys although out of the 5 I had they gradually went one by one until the last one perished after about 3 months. Everything else was fine but I blamed the gravel, the higher pH of my setup (hard water area) and I think they are a bit more sensitive than a lot of other fish. Needless to say I have not replaced them even though they are a really good addition.

 

[mark4785]

I also had problems with corys although out of the 5 I had they gradually went one by one until the last one perished after about 3 months. Everything else was fine but I blamed the gravel, the higher pH of my setup (hard water area) and I think they are a bit more sensitive than a lot of other fish. Needless to say I have not replaced them even though they are a really good addition.

 
They prefer a pH of 6.5 to 7.5 and a KH and GH of around 4dH. They like to filter sand through their gills, swallowing any food within the sand as they do so. Corydoras seldom go up to a pellet and bite chunks out of it which they would be forced to do if they have pea gravel (they cannot filter pea gravel through their gills).