What's up with this panda cory?

[Suse]

Hello all! My 72l tank is ticking along nicely, except for a panda cory issue. I bought 6 of them about 4 months ago, juveniles, seemed active and healthy. I noticed about a month ago that 4 had grown well and look adult size, but 2 had barely grown at all. One died sadly. The other tends to sit listlessly on the substrate rather than dashing around with the others, who are still very active. Photo attached, but the size difference is more obvious in real life.

Any thoughts? I'm puzzled as whatever it is seems to be chronic (stopping it growing), it's clearly not 100% but still alive. Other fish are little ember tetras, green neons and otos, who are all very healthy.

[black ghost]

Have you tried worming them?

That substrate is totally unsuitable for Corys, btw. They need sand. Gravel harbours bacteria which can be a problem for fish that live on it. Also they naturally dig for food, which they can’t do on gravel.

[Suse]

Thanks. It's not gravel, it's Tropica Aquarium Soil

https://tropica.com/en/plant-care/aquar ... rium-soil/

What would you recommend to worm them? I'll give it a try.

[black ghost]

For practical purposes it’s the same as gravel… too big to dig in, large gaps between the pieces, etc.

I always use Sterazin as a wormer. Others are available.

[Suse]

Thanks, I'll try Sterazin.

I can't remove the Tropica soil sadly. How much of an issue is it to keep cories on it? We can't get a second tank

[plankton]

The bigger one looks female to me and the smaller male....that may have something to do with the size difference as well.
Worming them won't hurt though.

[Suse]

Thanks Ian! What are your thoughts on the cories with Tropica soil? It's smooth rounded light granules. I know.you have pandas too.

[black ghost]

The really good thing is it’s not affecting their barbels at all. Rough gravel wears down the barbels and exposes them to bacterial infection (and probably hurts). So as long as you keep it clean like it looks now, it shouldn’t be a problem. Although they’d be happier on sand.

[Staffylover]

Some people I have seen make a sand pit area in their tank for the Cory, you would have to barricade the soil from it somehow, bit like a little beach area, seems to work well, all my tanks are sand on the top surface so I have not needed to try this myself, it is lovely to watch them snuffle around in the sand and it would be a shame if you miss out on watching this, sometimes they dig right up to their eyes!

[plankton]

I agree about having at least some sand (I won't have anything but sand nowadays), it is so cool to watch corys sifting it through their gills...that substrate itself shouldn't do any damage though.