Total loss of panda cories

[mightymouse]

My tank was set up 1 month ago, cycled and contained 15 panda corys with 15neon tetras. Tank size is slightly more than 1 ft.

Did my WC every 3 days with water conditioner (otto brand), however when i switched to ocean brand conditioner on sunday, and returned to office today, my panda cories all died, together with about half of my neon tetras, the rest of the survivors are too weak to last longer than 2 hours.

What puzzle me was that the cories bodies seems to melt, dissolving when i tried to clear the mess with my net.

My marimo balls also turned browned totally .

Water PH and nitrites level are normal (6.8 and 0), water temp (24 - 26)

i just wonder what had happened when i wash out the tank and salvage what i can. Now the tank is running again, but without any fishes, just a piece of wood embedded fern and a unknown plant that seems to survived and....i am just afraid that the new fishes will meet the same fate...

Wonder if any bros here can give some explanation. thanks

[k3nlim]

seems like over crowding to me..what substrate are you using?

[PKB]

That's a lot of fish for a 1 ft tank. What filter are you using?

[stormhawk]

We need the following information:

1) Size, type of filter
2) Substrate
3) Diet
4) Chlorine/Chloramine concentration in your tap water

Since your tank is located in an office building, it is possible that they died due to the following problems:

1) Overcrowding, because 30 fish for a 1ft tank is just too much.
2) Increased chlorine/chloramine content in your water, that was not eliminated by the conditioners
3) Bad food, or one of your colleagues tried to feed them with dire consequences without your knowledge.
4) Disease

That aside, I would suggest that you take pictures of the fern and the unknown plant for ID. It is possible that you have a terrestrial plant sold off as an aquatic plant, and which is probably leeching toxins into the water as it slowly dies due to prolonged immersion.