This is what I am using to try and get them to breed, a clear bowl, black/silver marbles, and a flowerpot with top and front hole in it.

I had these guys in their own 29 gallon tank with a bowl of marbles with the flowerpot over it (to try and have them spawn) yet after a good 8 months I got zero results.
I finally decided to just put them into my main 75 tank (since it is in the livingroom and i enjoy seeing them in there), yet still after a good year and half no spawning, i did try for a few months again to keep a bowl of black marbles in there with flowerpot over it, but after hours of watching them i never even see them IN there much less spawning.
I decided to put the bowl back in recently stil trying but curious what i might be doing wrong?
I got a few long tube/acorn-like catfish breeding things as well, again never once have i seen them IN it.
I know with having so many there has to be a male/female mix in there somewhere, they are very active little fish and are always scanning the bottom and sides of the tank, yet I have had ZERO success in getting them to mate in anyway.
PLEASE if anyone here knows what i can try or do let me know as I really like this fish but can't afford to buy more but really want more in all my other tanks in the house eventually.
My other fish (yellow labs, acei, red shoulders) breed like MAD so I know conditions for the fish are good, just haven't been able to get these catfish to breed to save my life...
Do I just watch that bowl of marbles till i see stuff at the bottom i assume are eggs then pull it and tumble the eggs?
I do check with a flashlight often but haven't seen anything in there that looks like iny eggs or anything.
Bill