Aquariums: I’ve never seen my Banjo catfish eat.

I’ve had a banjo catfish in my 70 galllon for a couple of years now, he’s gotten pretty big and is very fat! As with most banjos I rarely ever even see him in the tank, in fact I often go months at a time without ever seeing him at all and when I do it’s usually just his cheeky little mouth poking up through the sand.
Only thing is though I’ve literally never ever seen him eat! I put a couple of bottom feeder tablets in there each day but they are usually gone in a few minutes thanks to my large school of Catfish so I’ve never seen him eat those. I have no idea what he could be sustaining himself on because any food in the tank is gone immediately yet somehow every time I do see my banjo he seems bigger than before. He’s obviously getting nutrients somewhere but I have no idea how and when he would be doing that. It’s quite the mystery.