Dying Cory Cats

[squealor]

I had just finished cycling my tank with three serpae tetras, so we added a couple more serpaes and three really small Julii cory cats. They did extremely well for two days and I monitored the water closely.
Yesterday, I went home from work at lunch to find all the fish happily swimming around. When I got home from work just three hours later, one of the cats was on it's side on the bottom of the tank, barely alive. He tried to swim and only made it around in circles and spirals before crashing down into the gravel again. He was gone within a half hour. He had no visible signs of sickness (nothing growing on him, no sores, etc). The other fish still looked great.
I had to go out for a bit last night and when I got home, a second cat had the exact same symptoms (lying on his side, not able to swim straight) and he also died fairly quickly.
I tested the water: ammonia-0, nitrites-just starting to register, nitrates-5. They had warned us that adding more fish might start a mini cycle, but the nitrites are under .25.
The only other thing that I can find that is revelant is that the serpaes have been sort of picking on each other and the cats. They nip at the tail fins...
What could possibly be going wrong?

[Blizzard]

I'm not sure, but if you have any corys left I would quarantine them immediately...
-Blizzard

[Toirtis]

The nitrites will not help anything, so keep up on those water-changes. Its difficult to be certain just what is going on, but it does sound like whatever it is, is affecting your cats neurologically....now the most likely causes of this are bacterial and parasitical. By 'really small', just how big are we talking here?

[Jchillin]

Serpae's are a schoaling fish and are known to nip when they are kept in insufficient numbers. That is why they are nipping at each other and their tankmates. A schoal of 6 or more is necessary to eliminate the nipping.

As for the cory's, since they are bottom dwellers for the most part, suffer from the harmful parameters (the water at the bottom is always more toxic than the rest of the tank). All bottom dweller's would do better to add to a mature tank rather than one that is cycling.

[squealor]

Well, a few days later and the remaining cory is fine, despite not having quarantined him (this tank is brand new, I don't have a hospital tank yet). He's doing great, my water levels are great. No idea what happened to make the cats die.
The remaining one (and the others were the same size before they died) are about just under an inch....

[greenmaji]

has your water finished cycling?.. even durring the cycle.. I would recomend changing the water to keep NO2 down to 2ppm or less.. good luck

[squealor]

Yes, it actually finished cycling before we put the cats in, but adding new fish caused a mini cycle to occur. That mini cycle is now finished, too... Ammonia is at zero, Nitrites are at zero and Nitrates are around 5-10.

[Jchillin]

Originally Posted by squealor

Yes, it actually finished cycling before we put the cats in, but adding new fish caused a mini cycle to occur. That mini cycle is now finished, too... Ammonia is at zero, Nitrites are at zero and Nitrates are around 5-10.

That's good to hear. I would give it a couple of weeks before adding any more fish. This will prevent another mini-cycle.

[squealor]

That's what I'm thinking, too! And only add a couple at a time! Thanks for the help!