Odd Cory Behavior. Should I Be Worried?

[Linway]

Hey all,
So I have some Bronze Corydoras and for the past 24 hours their behavior has completely changed and I can't figure out why?
 
Normally my they are EXTREMELY lively, constantly swimming round turning over sand, looking for food or just being generally chirpy.
 
Yesterday I did my regular maintenance of using a gravel cleaner to get waste from the bottom and a 10-20% water change. Ever since then my corries just sit in a group together in the corner and then will occasionally swim to the top of the tank at quite a speed in that they jump out a little and then they swim back down to the same corner. I dropped in some catfish pellets and the did liven up a little to eat them but then they went back to this odd behavior.
 
I've tested the water conditions and everything is as it was before:
 
Ammonia: 0ppm
Nitrite: 0ppm
Nitrate: ~20-30ppm
pH: ~7.4
 
In fact while typing this I've just noticed one of the corries swam to the top and jumped out 3-4 times before returning to the corner, in fact it's just done it another 2 times.
 
What on earth is going on?
I'm watching them right now and they are just sitting in a corner, swimming to the top to jump and then go back down.
 
The only way I can describe it is it looks like they are attempting to catch flies (no there aren't any flies) lol
 
Please help I'm really worried!
 
I should say what ever has changed is only affecting them, in the same tank I have neon tetras, platys, bristlenose pleco, red cherry shrimp and a betta, and none of their behavior has changed, it is just the corries.

 
Oh also, I made one change to the tank in that I removed an ornament from the tank as it was causing problems with the sand, but it wasn't an ornament I've ever seen them interested in.
 
Finally, I've just recorded a 10 second video and uploaded it to YouTube for you guys:
http/www.youtube.com/watch?v=pSwszkBVzeM
 
Thanks guys and I hope someone can help

 

[Fishmanic]

they are going to the top to take a gulp of air---make sure you have good aeration (via airstone and/or water drop if you have a HOB filter--if all water parameters are fine and the other fish are fine, there''s not much else you can do but wait

 

[Linway]

But why would their be a problem with aeration now? I've had them for about 4-6 weeks or so now and they have never done this until this last 24 hours?

I'm not saying you're wrong or anything by the way, I just want to understand this.

 

[Ninjouzata]

What is the temperature of the tank?

 

[Linway]

26oC

 

[Ninjouzata]

Hmm, I don't know I was thinking maybe if the temperature had risen without you noticing, increased heat leads to less oxygen in the water, right? Seems like a normal temperature to me though. I hope someone can figure it out for you soon!

 

[RCA]

Corys do go to the surface to gulp air, you may just not have seen it before.  When your Corys dart to the surface they take in air and then absorb it through the wall of its intestine, which is then released via the vent.  I believe they have adapted this form of breathing over time to manage low-oxygen waters.  So it is normal behaviour.  However, if it is more than usual it maybe that when cleaning the substrate some "toxins" may have been released, but this would depend on how deep you went with your cleaner and whether you did the whole of the tank at the same time?  I generally tend to clean my substrate in sections so that it limits the disturbance.
 
How long has the tank been set up and how long have you had the Corys?  Are they still feeding?  What filtration is on the tank?
 
The other thought is, if the water added back into the aquarium was slightly lower in temp. than what was in the tank, it can stimulate breeding.
 
TBH it is difficult to say exactly if there is even a problem, they may just be adjusting to the water change.  Just make sure you have plenty of oxygen going into the tank and keep us posted.

 

[Linway]

Hmm, I don't know

I was thinking maybe if the temperature had risen without you noticing, increased heat leads to less oxygen in the water, right? Seems like a normal temperature to me though. I hope someone can figure it out for you soon!

Nah the temp hasn't changed, I have a regulating heater which only turns on when the temp drops and the weather has been nowhere near hot enough to raise the temp of the tank (it's currently 2 quilt weather haha).
 

Corys do go to the surface to gulp air, you may just not have seen it before.  When your Corys dart to the surface they take in air and then absorb it through the wall of its intestine, which is then released via the vent.  I believe they have adapted this form of breathing over time to manage low-oxygen waters.  So it is normal behaviour.  However, if it is more than usual it maybe that when cleaning the substrate some "toxins" may have been released, but this would depend on how deep you went with your cleaner and whether you did the whole of the tank at the same time?  I generally tend to clean my substrate in sections so that it limits the disturbance.
 
How long has the tank been set up and how long have you had the Corys?  Are they still feeding?  What filtration is on the tank?
 
The other thought is, if the water added back into the aquarium was slightly lower in temp. than what was in the tank, it can stimulate breeding.
 
TBH it is difficult to say exactly if there is even a problem, they may just be adjusting to the water change.  Just make sure you have plenty of oxygen going into the tank and keep us posted.

Well i had a very heavy ornament in the tank which was causing a dead spot in the tank and the sand had turned black so when I did the maintenance and noticed this I removed the ornament and was extremely thorough with cleaning the sand to remove any black sand so the sand was very disturbed, but to be honest every time I clean the sand I go quite deep with cleaning and they have never done this before.
 
Off of the top of my head I set the tank up about 3 months ago, did a roughly 6 week fishless cycle, started the tank with platys and tetra to ensure everything was OK and then I put the corys in about 4 weeks ago. That's what is most confusing to me is that they have been in a while that the behavior has changed, not the jumping as much it's more they were extremely live and would swim in groups where as now unless they are jumping they just sit still and are never in a group. They are either in pairs or solo.
They are still feeding, I dropped some catfish pellets in to see if they would wake up a little yesterday and they instantly went for the pellets, ate them and then went back to being still.
As for filter, I have this: http/www.creativepet.com/images/hg10287.jpg
 
I read about the possibility of breeding but tbh I have no idea of the gender of the fish, and from what I've seen of cory breeding behavior they don't seem to be doing any of it (males chasing females and then sitting in a T shape).
Looking at the tank now, one of them seems to be a little bit more alive but the others are still just sat separately only moving to "jump".
 
But as I said it's not the jumping that worries me, it's just the complete change in behavior.
 
Also I dunno if it helps but what ever is causing this is strong enough that it affects all the corys, but not so strong that it bothers any other fish as they are all perfectly normal (even the pleco is fine (I say the pleco as that's the only other form of catfish I have in there)).
 
Cheers guys

 

[greenmumma141]

I would ask if you forgot to add dechlorinator, but by now I'm sure you'd have much bigger problems.
 
TBH, cories are confusing little things. For the first year that I kept cories, I was always running to the tank going Oh no, why are they swimming aound like that, oh no now they're not swimming anymore lol.  I'm not saying you shouldn't watch their behavior, bc they're great little alarm bells if there is anything going wrong in your tank, especially where oxygen is concerned like RCA said. 
 
I would say the bacteria from the black sand is causing them to act listless, maybe do another wc if their energy hasn't returned.
 
Every time I've ever purchased a cory (especially green/bronze) they go bonkers in my tank for the first month or so, darting around and swimming all over the place. Then their behavior will change, sometimes very fast. Then they'll just sit around with the other cories. They still swim and dance, but not all the time. This could be something thats happening too.

 

[DoubleDutch]

Keeping 4 kind of bronzespecies. 3 of them hardly go for the surface, but one (Emeralds) almost jumps out of the water whenever I feed them.
Nothing unusual about that but it could be a sign of stress in this case (changing waterparameters), starting so suddenly. 
Sometimes they even gulp too much air when stressed and will start to fload. The black spot in the sand could also mean anaerobic bacteria with some chemical residu they made. Possibly they react on that !!!
I think it will settle down, but just keep a close eye on them an on your other fish. If / When they start to act strange as well, their may be a bigger problem.

 

[Linway]

I would ask if you forgot to add dechlorinator, but by now I'm sure you'd have much bigger problems.
 
TBH, cories are confusing little things. For the first year that I kept cories, I was always running to the tank going Oh no, why are they swimming aound like that, oh no now they're not swimming anymore lol.  I'm not saying you shouldn't watch their behavior, bc they're great little alarm bells if there is anything going wrong in your tank, especially where oxygen is concerned like RCA said. 
 
I would say the bacteria from the black sand is causing them to act listless, maybe do another wc if their energy hasn't returned.
 
Every time I've ever purchased a cory (especially green/bronze) they go bonkers in my tank for the first month or so, darting around and swimming all over the place. Then their behavior will change, sometimes very fast. Then they'll just sit around with the other cories. They still swim and dance, but not all the time. This could be something thats happening too.

Nah I definitely didn't forget dechlorinator, I know because I used the last of the bottle and I need to go by more.
I'll do another water change tomorrow if there is still no change.
They are bronze corys so maybe that's what is happening in that they went crazy for a month and then just settled down? Thing that concerns me is that it doesn't seem like they are resting, it seems like they are in some sort of trance lol. I want my spazzy corys back!

 

Keeping 4 kind of bronzespecies. 3 of them hardly go for the surface, but one (Emeralds) almost jumps out of the water whenever I feed them.
Nothing unusual about that but it could be a sign of stress in this case (changing waterparameters), starting so suddenly. 
Sometimes they even gulp too much air when stressed and will start to fload. The black spot in the sand could also mean anaerobic bacteria with some chemical residu they made. Possibly they react on that !!!
I think it will settle down, but just keep a close eye on them an on your other fish. If / When they start to act strange as well, their may be a bigger problem.

Yeah none of the other fish have even slowed down or changed in anyway... I mean I noticed one of the tetras being a bit aggressive to the other tetras but that's nothing new really.
Just looked at the tank now and they are all sat together at least so they aren't going solo anymore which is good I guess.
 
I guess I'm just overreacting and with being a new fish keeper lol
I'm taking some water to the store where I got them from and going to ask them to test it for me just to make sure everything is ok. API Master Test Kit is good and all but its very hard to compare colour charts so better safe than sorry.
 
Thanks for all the advice guys, much appreciated as always!
 
EDIT:
Ok so I just looked over at the tank and got horrifically scared as I could see a cory tail but nothing else, I thought something had eaten the rest of him. Anyway turns out he had just buried himself under the sand? Do they do this? I've never seen any of them do this before.

 

[Shaddex]

Silly question, but have you added any other fish to the tank ?

 

[IonaMcCluskey]

read the thread/poll about sand, gravel or bare bottom.
there is info from tcamos at the end of it about sulpher poisoning, it may be something like that seen as you mention blac sand.

 

[RCA]

+1 what greenmumma... says about doing another small water change.
 

 
 
I want my spazzy corys back! 

Then get some Albino's they are madder than any other Cory 

 
 

 
EDIT:



Ok so I just looked over at the tank and got horrifically scared as I could see a cory tail but nothing else, I thought something had eaten the rest of him. Anyway turns out he had just buried himself under the sand? Do they do this? I've never seen any of them do this before.

Yes they do seem to bury themselves in the sand as I have mentioned with my new Cory's here.  Also, I had a similar scare in my other large tank only last night when all I could see of one of my Albinos was his dorsal fin and a little bit of his back.  I went to get the camera to capture this behaviour when up it popped!
 
Out of interest what dechlorinator do you use?  I switched some time ago to Seachem Prime, it is more expensive, smells like ?, but is economical so you only need a small amount.
 
Sometimes it can also be a change in water chemistry that can cause the fish to change behaviour as our water companies add different chemicals within the purification process.
 
I am sure all will be well, they are just being Cory's, but as before I would agree, that if you are concerned, just do another small water change.

 

[greenmumma141]

One of my cories stayed burried for so long, I was about to pull him out with my tweezers, I thought he had to have been dead. Then he just popped up and gave me a "Do you mind?!?" look and swam off. lol again, they're very odd little fish and their behavior will keep you guessing all the time.  Try not to sweat the small things with them, bc if they is something major going on, it WILL be very obvious with their behavior.

+1 what greenmumma... says about doing another small water change.
 

 
 
I want my spazzy corys back! 

Then get some Albino's they are madder than any other Cory 

 
 
 .

 
So here's a question... If I want to get albinos, would albino c. aeneus shoal with my green cories? or would I need 6 of them???