Burrowing catfish compatibility with differing grain size?

[Tacocat]

Has anyone found that their burrowing catfish having difficulties digging in pool filter sand? I'm currently keeping 4 wild-caught Pseudohemiodon sp. Peru II (also known as P. almendarizi) and I noticed that only the smallest fish is able to do the classic pseudohemiodon shuffle dig and cover itself in sand. I've seen the larger individuals attempting to dig resulting in a pitiful amount of sand being moved. Even after adding more sand to their hangout zones they still didn't seem able to do anything.

I suspect that it probably has to do with the larger grain size of pool filter sand compared to the naturally fine grains of their wild habitat, as over time the larger fish seem to have improved, but it's still suspicious how quickly the small guy got the hang of it.

Anyone else seen this with other fish?

 

[GaryE]

Any bury themselves cats I've kept have been in fine grained sand, not coarser pool sand.

 

[TwoTankAmin]

To confirm what GaryE wrote, here is what Planetcatfish says"

Sand on the bottom so the fishes are able to dig themselves into the substrate. When feeding they filter through the substrate and so the size off the substrate should be very fine.

from https://www.planetcatfish.com/common/species.php?species_id=4224