Substrate observations

[raylove]

I recently bought 10 (false) julii corys, the first time I've had corys for over a decade. Back in the day I didn't know any better so previously I've only kept groups of 4 and only ever with gravel substrate. This time I did it properly, bought a larger group and converted about 20% of the floor of my 55 gallon to sand.
2 weeks in and these are my observations:
For the first couple of hours they kept together in a group but once settled there are now 4 that hang out together most of the time but the other 6 are loners - they forage, glass surf and rest pretty much alone. I guess in a tank they are close enough to be aware there are others close by, but I'm not seeing the social interaction I was expecting.
The biggest surprise though is the substrate. They almost never venture on to the sand! Even when swimming from one end if the tank to the other they seem to actively avoid the central sandy area by swimming around it. I have only seen one fish briefly forage in the sand just once - certainly no 'sand sifting' - whilst on the other hand, they poke around in the gravel all the time. My impression so far is that given the choice, they seem to prefer the gravel.
I'll give it until they mature but tbh I don't like the look of the sand as much as I thought I would, so if things don't change I'll probably ditch it.
This is quite interesting too:

 

[CassCats]

First off this video is proven to just be corydoras in a transient waterway, they migrate between suitable habitats. This video is full of misinformation and Ian Fuller has also disproved this video particularly.

Second, if there's more cover on the gravel side in terms of plants and decor, they'll choose that as 2 weeks in is still settling in and are likely to feel more uneasy about open spots.

They should always be given the option to sift, regardless. Gravel traps more bacteria under it, and while most fish don't come into contact with the bacteria level there, corydoras who dig in substrate to eat, DO. Even a small cut on their barbels comes in contact with this bacteria and in turn it becomes infected and the fish lose their barbels. It's why gravel is a poor substrate choice for them health wise. It's not just a matter of it being sharp or whatever not, it's a matter of other factors.


Hoplisoma trilineatus are a slightly more cover-happy cory species. They aren't huge on spending a lot of time in exposed areas, they'll rest under wood and among plants. Even leaf litter if you add that as well

 

[TwoTankAmin]

 

[MaloK]

Water flow is the key.

Any Cory need 3 different layers of possible activity... Not that easy to achieve in small tanks.... Any imo.

But that all relies on water current.

1: slow, more near to not moving water, in the center area. Cories still requires a lot of rest, need some quiet places. And a lot of exits where they hide.
2: medium, near the bottom, where you feed them, cool places to be, facing a slow persistent front current...
3: high, near the top or middle of the tank, Where they can compete and have fun playing with each other...

If you can achieve the water movement required and enough resting place at the same time.

Boom !

Don't worry about substrate, they are going to get used to everything, and have their preference.

You're giving them too much choice.