What's Up With My Corys?

[Tu13es]

I bought four Corydoras Rabauti (rust cories) about a month ago. A few days ago I was away for about 48 hours. Upon coming back, I found one of my corys floating at the top of the tank, dead.

Now, the remaining corys don't seem to be acting normal. The three of them seem to spend a lot of time resting on the bottom, particularly under decor or plants. Sometimes they'll swim around a little (one of them in particular has been more active), but the other two seem pretty calm. I'd been feeding them algae wafers and today bought some frozen bloodworms for them. The corys didn't seem to care much, though they were in a spot where not many bloodworms reached them. I tossed in an algae wafer and they nibbled on it, but didn't seem as active about it as normal. They generally go nuts when I feed them.

Also, I'm not sure if this is just me or not, but they might seem a little darker on their head/nose than normal. I'm not sure if this is true or if my mind is playing tricks on me.

Some more info on my tank: It's a 29 gallon tank, with 6 zebra danios and 2 amano shrimp. I have a few live plants and snails as well. I tested the water yesterday and it read either 0, or just slightly above for ammonia, nitrites, and nitrates. pH is 7.2. Chlorine is 0. I generally treat with Prime before adding water. I did a 30% water change/vac yesterday.

Any ideas?

Update: Another cory died. See below.

 

[Inchworm]

There is something wrong with your beneficial bacteria. You should have some nitrAtes show up when you test. I'd do some water changes (using a plain water conditioner like API) to get rid of the Prime and see what happens.

What temperature do you keep the tank at? What kind of substrate do you have?

 

[Tu13es]

There is something wrong with your beneficial bacteria. You should have some nitrAtes show up when you test. I'd do some water changes (using a plain water conditioner like API) to get rid of the Prime and see what happens.

What temperature do you keep the tank at? What kind of substrate do you have?

Hm, interesting. I've never had much of a nitrate reading. The tank is about 3 months old.

I'll see if I can get a different water conditioner tomorrow.

The tank is at about 75F right now. The substrate is small pebbles.

 

[Truck]

low nitrate is normal and a good thing, plants or anaerobic bacteria will use nitrate.

 

[nosoup4you]

He has quite a few plants in his tank so the lack of nitrate isn't too alarming.

 

[WILDER]

If you have a slight ammonia reading I would cut down and feeding and do a water change.
Corys are very sensitive fish.

Do any of the corys look bloated.
Check there tummy for sores, or red streaking.
How do there barbals look.
Being listless, lethagic, and darkening in colour can be symtoms of a bacterial infection.

Need to improve there diet with frozen brime strimp, daphnia which helps the fish digest its food.
Introduce some green veg into there diet like broc, cabbage, spoats, lettuce, cucumba, and finally peas which are good for keeping the fish going to the toilet.

 

[Inchworm]

Hi Tu13es

You should have some nitrate reading. The Prime might be interfering with that. Your water temperature is good for those corys, so that's not the problem. Were these corys in the tank when you cycled it, or did you do a fishless cycle? If there were ever any ammonia or nitrate spikes it could have caused them harm that is only becoming apparent now.

 

[Truck]

0 nitrate is perfectly normal, plants will use nitrate in photosynthesis, and also anaerobic bacteria can colonize in the substrate, they take the nitrate and take the oxygen molecules and then release the nitrogen molecule and the nitrogen will gas off.

 

[Inchworm]

Not likely in a 3 month old tank with "a few" plants, truck.

I'd hold off on the veggies, Wilder. Corys might nibble them, but they aren't part of their regular diet. I think there would be a risk of polluting the water that would be greater than any benefit they would provide. A good quality flake food, that contains some algae, would be better for them. Hikari sinking wafers are excellent if you can get them.

 

[Tu13es]

Not likely in a 3 month old tank with "a few" plants, truck.

I'd hold off on the veggies, Wilder. Corys might nibble them, but they aren't part of their regular diet. I think there would be a risk of polluting the water that would be greater than any benefit they would provide. A good quality flake food, that contains some algae, would be better for them. Hikari sinking wafers are excellent if you can get them.

Hikari algae wafers is what I've been feeding them.

For plants, I've had an anubias nana and java fern for a month or so. I also recently added a couple crypts, java moss, and subwassertang.

I did a fish-in cycle with the zebra danios and added the corys after two months.

 

[WILDER]

Thanks inchworm never knew corys didn't have to have veg. I mainly feed them for the other fish.

So the tank had cycled when you added the corys.

 

[Tu13es]

I bought three more corys last week. I went away this weekend and found one of my old corys dead in my filter intake. The corys I bought last week have gone from a bright white color to much darker. One of them has a dark green spot on the inside, it seems. Also all but one of the corys (the one with the greenish color) seem to be pretty inactive in general.

I did a 15%ish water change and vac yesterday. 0 Ammonia, nitrites, and nitrates. pH was about 7.4-7.6.

Any ideas? Bacterial infection?

 

[Tu13es]

Gah! Just went to check on them and one of my cherry barbs was dead stuck to the filter intake. And I can't find two more of my cherries. ####.

 

[Tu13es]

Okay, I talked to Tolak and I am going to start doing large daily water changes and possibly treat with Maracyn I/II. Any other thoughts would be appreciated.

 

[WILDER]

I agree. Water changes and bacterial med.
Good Luck.