Happy panda demise - help

[ross1219air]

I am helping my neighbor set up her aquariums. We are having deaths of apparently healthy, happy Corydoras pandas.
The tank setup is:
- 20 Gal (24"W) tank
- Power filter with bio-wheel
- Tank cycled with two Rasbora borapetensis
- Setup for 5 months
- rocks, driftwood, and plastic plants
- 1/4" rounded gravel
- pH 7.3
- Ammonia 0 ppm
- Nitrate 0 ppm
- Nitrite 0 ppm
- dGH 8 deg (143.2 ppm)
- distilled water
- heater, temperature steady 75 F
- 20% water change every other month
- fluorescent light 8 hours per day (13:00-21:00)
- water color slightly brown (from driftwood tannins presumably)
- flake food and algae pellets (not overfed)

After a 3 week quarantine, 2 Corydoras panda where added to the tank 2 months ago (a third panda died during quarantine - apparently caught in a plastic plant). Both the new pandas, and the existing two Rasboras seemed to thrive for the first 1-1/2 months. Then, just minutes after the pandas had been observed acting normally, one was found dead - with no apparent disease, distress, or trauma. Now, about 2 weeks later, the second panda died the same way - seemed fine, and then found dead an hour later.
Possible factors?
- There was thick white fungus on the driftwood that the pandas occasionally liked to eat. Could something in this have been toxic?
- The second panda died 1 day after about 1 quart of distilled water had been added to make up for evaporation. Something in the new water the panda is sensitive to?
My neighbor loved the pandas; they were very cute and entertaining, but is very distressed at their sudden deaths. Can anyone offer any help?
Thanks.

Ross :)

[NEON98101]

I'm sorry to hear about the Panda.
Yes, I think they are great. I have 7 breeding group and some eggs and lots of frys. I am not an expert of water condition. But it seems all the reading is nothing out of ordinary.
I did lost 1 out of the 8 I originary purchased from the store. She develope this breathing difficulty after I had her for a month. And lost few frys while raising them but I think they were genetically weak and not to fit to go on.
Anyway, I can't have absolute answer for you. Except some possibility.
Sometime, some chemical fume like paint or house hold cleaning chemical or even some chemical air freshner could cause adverse effect to the fish. Like some mist from the hair spray or bag spray etc. Or maybe some residue of soap or detergent got in the tank. I heard this horror story about the fish died because the neighboor had some house painting and I guess wind was blowing wrong way before.
Or it could be simply they died from the old age. Since I have been only keeping Panda from January. I have no idea how long they expect to live. But I think they reach to their max size at 1 1/2"(TL) and my 3 months old is already 1 1/4". So I expect them to be 1 1/2 " in another month.
It sounds like a quick death, I suspect some kind of chemical poisoning. But like I said, it is just a guess.
Unless you send the dead body to the lab to examine, you would never know the cause. But I believe your water condition is not anything close from the dengerous. Although I am not the person to say since I only got the ph test kit but nothing else. I just do the water change often and feed them well with variety of food. After all, they are either breeder or growing fish.
I hope you can solve the mystery or you can find the hint from my thought.
And I'm sorry about the fish but nothing live forever.

[ross1219air]

Neon98101,
Thanks for sharing your thoughts. I think they were young, about 3/4" TL. I will check if perhaps the area had recently been cleaned. Do you know if the flake food and spirulina (sp?) pellets are appropriate food for the pandas?

[NEON98101]

I don't know about the flake since I don't know the content of it. But spirulina (sp?) pellets is not for the corys, little may not hurt them but that is for the plant eating fish. Corys do need more meaty food. They like worms and live food. I do feed many worms, grindel and/or white and even microworms. I'm not crazy about I even sometime chop up the earthworm I culture. You can find the earthworms in garden but you have to make sure there are no pesticide or any dengerous chemical where they are collected. You can feed some hardboiled yolk from the egg but use sparingly since they can foul water and messy. Or you can feed some chopped raw shrimp from grocer, I hear they like that. Mine get some dried kril. They also like live food like brine shrimp, I hatch them. And Daphnia, I got some from fellow Aquarium society member's pond. And of course, you can get some frozen fish food from the pet store. Or pellet or flakes but make sure the main ingridient is meat and not a grain or vege. Cory is meat eater. Mine like home made beef heart mix. This is old fish receipe, you can get on web.

Anyway, they like meat. And like to eat. I bet mine would eat all day long if there are food. Of course, mines are breeder and growing youngs. You can feed them a lot but make sure the water quality stays high. I do partial water change often since I feed them often and well.
I hope you can keep your Pandas healthy. They are cute and funny such a character.
I got in this FULL time hobby for tetra especially Neon but now I really love my Pandas.
I can't get tired of watching them. Yeah, Neon is pretty but cory sure got personality.