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Hi guys, within the span of two days 5 of my 6 cories have gone belly up....and the one remaining isn't looking too good. I checked for nitrites and ammonia, both are 0... I do 10% daily water change (it's a heavily planted discus tank) so the water is clear. I do have some algae on my leaves but the rest of my fish are doing fine... The discus are eating like little pigs and have wonderful coloration...

Any ideas? I'm at my wits end... Thanks!
 

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How long have you had the cories? Were they eating? what were you feeding them? how big is the tank?

Do they have barbels? what is the water temperature?

Despite some people saying domestic cory can handle warm water, pepper and panda cories prefer cooler water around 73-77f.

Sterbai, Gossei, and Adolfoi are the few cories capable to the warmer water. 82f

10% water change will not improve anything. You are better off doing 50% water change weekly.
 

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Discussion Starter #5
Cories

Turtlehead, yeah nitrites are supposed to be 0, didn't test the nitrate level but they should be normal...

The cories have been doing fine for the past 2-3 months. Food are flakes and frozen blood worms, same food as the rest of the tank. Tankmates are rams, dwarf gouramis, neon tetras and 4 juvenile discus.

Temp is at 28-29C. Discus were tank raised without heaters so I don't use one either.

I checked the dead corys and yes, they still had their barbels. I do 10% daily w/c after feeding the discus and and 50% weekly water change during the weekends when I clean the tank, scrape algae, etc....

I'm hesitant to add more corys till I find the cause of death of my fish. I've heard that they're sensitive to water quality but my other fish are doing well and my discus are eating like pigs and have wonderful coloration....

Puzzled...
 

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Huh, that's a little odd since your Discus are thriving. I don't think Cory's are as sensitive as Discus are. :???:

Do you feed them bottom feeder tablets or anything the other fish can't get? If so, perhaps you got a bad batch of food and they are the only ones chowing on it.
If you don't feed them anything right before lights out, maybe they're just not getting their share of what you do feed and they're starving... I doubt it, but just trying to toss a few ideas out.

Keep us posted.
 

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The Pandas are especially delicate fish, for some insane reason, and are really sensitive to not only water quality but water quality changes. We had three Pandas kick within two days a few months back, after they'd been in the tank for well over a month. Nothing changed, and the water chemistry was all good (though the pH was around 7.5). It looked like they basically starved, as they spent most of their time hiding. OTOH, the remaining three Pandas have always been more active and social and have eaten like pigs, and are still doing well. They shoal with the Corydoras julii, and one Panda in particular seems to have a major crush on one of the Julies.

The Peppered Corys (Corydoras paleatus) do a lot better in much cooler water, according to the Big Boys and Girls Who Know More Than I. They want a top temp of 24C, or they get really stressed. Seems a bit weird for such substantial-looking fish, but they apparently over-rev and basically burn themselves out in warmer water. I saw this info in three separate sources, so guess it may have some credence. That's the only reason I don't have any, and went with the C. julii instead.

Good luck, and if you're looking for another good small Cory the Julies are tough little cusses. Top out at 55mm, though mine are all more like 45mm.

HTH
Glen
 

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You say you're keeping a discus tank, and to me this implies hotter water than average. What temp are you running at? A lot of cories need cooler water than we suppose to do well and thrive...anything above 78 and most of mine aren't happy. There are a few exceptions, like C. sterbai, that do well in discus-type water.
 

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I've had good luck keeping Cory's like Adolphois, Melini's, Schwartzi's and others in 79 - 80° temps.
One of my tanks runs around 81° and the little buggers spawn like crazy. :?:
I guess I didn't realize temp was such a big issue with Cory's, but you learn something new every day. :) Maybe mine are just defying the rules, since some of them are around 8 years old and have always done well with the higher temps.

I'm wondering if the Cory's in question are suffering from heat, since the tank doesn't have a heater, though.....
 

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Was at a fish club talk two weeks back (SVAS) and the speaker was discussing fish collection trips he has done throughout the Rio ***** and Rio Xingu region for plecos. He commented on how surprised he was that he never saw cories in stagnant water. They always congregated in the shoals and areas of high current. A locally successful cory breeder said when he wants his pandas and adolphois to spawn he turns on the Rio’s on the end of his tank to make current and drops temp from 78-80 to around 72-74. Mine have been grown from 10mm to adults in 82-84F water.

I keep 6 pandas with 8 discus in a 75g long tank. It is heavily planted with CO2 injection. It has a light cross current from the canister and a Rio 400 that runs my CO2 reactor. The one thing I have noticed, is that when I get drops in my oxygen saturation (it’s way overstocked now) from either the filter clogging and current slowing down, or too much sat CO2 that the pandas start gulping for air, and snorkeling long before the discus too. That points out to me that in my setup, the pandas are more sensitive to poor oxygen levels than the discus are. Air stones help but water movement increases oxygenation better.

I spent a long time searching a reading online about cory health and water needs and the one point of consensus was that water quality is more important than specific parameters. Is the water hardness fairly normal or are you using a purposely soft RO mixture? We have really soft water here in Oakland, kH 0-2 and gH 3-4. I don’t need to use RO but the water is so thin I have found I needed to increase it’s “other” minerals by adding Seachem Equilibrium , and Kent Freshwater Essentials to increase to 4-5 kH and 7-9 gH. This can also be done with RORight and DiscusBuffer at slightly higher cost. This really improved the color of my discus. After discussing with several discus owners and local breeders they all felt that our water didn’t have enough total dissolved ions to avoid getting brown blood disease when nitrite levels increased from time to time as my filters clogged and my plants weren’t taking it up.
 
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