small cories dying

[Fletch]

I have a pretty newly set up tank (36"x12"x18") which I cycled with Platies. Cycling finished 2 weeks ago. The next day I added 5 peppered cories which were about 3/4" long (tiny). A few days later I added 8 zebra danios, then a few days later 7 lemon tetras.
I am feeding them all the New Life Spectrum small fish formula. When I put food in there it is like a wild feeding frenzy. I try to add enough, though, that some gets to the bottom, which is gravel (not too fine, but not coarse either, probably 1/8" to 1/2" diameter).
It has always been tricky to find all 5 of them since they don't tend to stick together. However, yesterday I could only find 3. One seems to have died and disappeared, and I found one lying on its side behind a piece of driftwood. He was incredibly skinny and unable to move normally. Of the other 3, one is still pretty small and the other 2 are about twice as big as him.
I'm fairly certain the problem is food -- that the cories just aren't getting enough, or at least that some of them haven't learned to get the food that falls in the gravel. I realize that maybe the pellet size is too small for my gravel (ie, it falls between the rocks), at least for really small cories.
My question is, how do you feed really small cories in a community tank with lots of other ravenous fish? Or, do you just avoid the little guys, or keep them separate until they're bigger? Is there a particular kind of sinking pellet that will work? (I'm just afraid that no matter what I get, my other fish will hog it all anyway).
Thanks!

[bitterman]

Sounds to me like our tank might be cycling again. What are your ammonia, Nitrite and Nitrate readings?

Even though the tank was cycled with the platies when you add more fish, it puts more load on the nutrifying bacteria. This can cause your ammonia and Nitraite to go high again and cause fish stress/death.

You can also try other foods that are larger and they can feed on like cucumber zucchini or even shelled peas. Another option might be spirulina tablets/wafers or shrimp pellets

Bruce

[Fletch]

Hi Bruce,

I've been checking my NH3 and NO2 levels almost daily, and they're always zero.
NO3 is never above 10 ppm. So I don't think it's a cycling issue.
I'll try some of those suggestions.
Thanks.

[exv152]

I have corydoras duplicareus (which are smaller than your average cory) together with peppered cories, and sterbai, altogether I probably have 15-20 in a 125g with larger more aggressive fish (SAEs/angels etc). I find cories need sinking pellets for bottom feeders to get their fair share of food, and I feed them at the same time as I feed flakes so the more aggressive fish are distracted from the pellets. I also place pellets at opposite ends of the tank for the same reason.

[mm]

If you want a microworm culture I can start you one. Just pm me.
Not sure if your problem is lack of food but the microworms sink to the bottom and the cories should get their fair share.

[lucius]

I feed all my cory's after 9:30 pm.  The lights are off at that time and the rest of the fish are starting to sleep.  I'm feeding them Omega One Shrimp Pellets and Hikari Algae Wafers.

[sas]

Definitely feed after lights out. Mine are always feeding when the other fish are quiet.

[101DalmatianMollies]

I had one small Cory in amongst 3 larger cories. I started feeding frozen brine shrimp and frozen bloodworms alternate days and my small guy had a huge growth spurt and is now the same size as everyone else. It keeps my tetras happy too, my assassin snails as well as my pleco who seems to sample from them as well. I also do sinking alge wafers for their veggies. Treating my tank currently for cyano with hydrogen peroxide which makes the cyano tasty after it's been mostly killed so my pleco and cories eat that up too. Not that you should get your tank overrun with cyano lol!