Hi all,

I have had a 20 gallon tank that has running for the past 4 months, and I have recently begun experiencing a die off among my panda corys. In the past week, 4 out of the 7 that were in the tank for 1-2 months have died rather unexpectedly (one did have popeye, but the rest looked and behaved normal), and I am quite perplexed.

Here are the current water chemistry properties:
Temperature: 77 F
Nitrite: 0 ppm
Nitrate: 15 ppm
Hardness: 150 (GH) ppm
Alkalinity: 40 (KH) ppm

Other tank dwellers:
2 oto cats that appear to be healthy, though they have become rather shy.
4 zebra danios that also appear to be healthy and are quite active, though one is very fat and I am slightly worried it may have dropsy.

Anyone see anything that might be the root of the problem? Thanks for the advice.

How often and how much water changes do you do? Popeye is a sign of poor water quality. What are your ammonia and nitrite levels?

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220 Tank build
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I do a 25% water change weekly. I just re-tested ammonia and nitrite, and both were at 0 ppm.

I was originally thinking it may be a water quality issue as well, so I started testing every other day to see if there was some sort of drastic decline that happened midway through the week, but the water quality seems to remain pretty stable throughout. Just in case, I changed the charcoal filter about 2 weeks ago and cleaned out the sponge filter two days ago. I also began a melafix treatment yesterday in the hopes of helping out any external infections.

Cory's don't take well to aquarium salt. If your using that to treat your other sick fish u might be stressing them out.

Do you treat your water with anything prior to adding it to the tank? What is the pH? Do you have any plants or decorations? Do you ever vacuum the bottom gravel? Does the tank surface smell at all? One thing could be compacted gravel and H2S build up, but this is usually rare.

Have you seen all your fish eating recently?

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--->Pictures of my 75g Amazon tank<----

Interesting points so far. Thanks for the responses.

To mk4gti:
No, I have not been using salt in the tank so as to avoid causing any problems for the cories.

To Dmaaaaax:
I treat the water with API water conditioner prior to adding it. The pH sits pretty steadily between 7 and 7.2. For tank decorations, there are a few plastic plants and a fake piece of rock (supposedly non-reactive). The bottom gravel gets vacuumed with each water change, and I don't notice any peculiar odor from the tank that seems out of place.

But, now that you have mentioned it, I have not seen the cories eating recently. The surviving three do scuttle about the bottom of the tank looking for food, but I rarely see actually settle and dig into anything. The have access to any flake food that is left over from the danios, and I usually throw in a half of a sinking pellet or algae tab at night.

Cories aren't algae eaters and will only eat it as a last resort. Try giving them some sinking shrimp pellets.

__________________
SUCCESS IS MEASURED BY YEARS, NOT MONTHS!!!
220 Tank build
http://www.aquariumforum.com/f15/sta...late-3253.html

Varying their diet is a good idea. I'll drop by the local pet shop tomorrow and see what tasty morsels I can pick up for the cories.

Probably not really an issue with you only changing 25%, but if your water has Chloramine instead of chlorine, the API conditioner will bind up the chlorine, but leaves the amine which is ammonia. Other conditioners will take care of both chlorine and ammonia, and other toxic chemicals/hard metals.

Good luck with your corys. Hopefully they just want more food options though. Remember if you are feeding flake food to pinch some then dip your fingers in the tank to moisten it so it will sink to the bottom. Mine typically scavange for blackworms that "escape" the feeding trough and then try to bury in my gravel.

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--->Pictures of my 75g Amazon tank<----