I do use blanched zuke, the oto makes use of that regularly. I also use algae wafers. Blanched cuke. I tried blanched edamame (shelled) but he never went near that.
I had tried the growing on rocks in the jar, which is how I got the weird looking thing initially. No success 'growing' algae, the jar is now washed (bleached) and back in the cupboard, the rocks also cleaned up again, and sitting waiting for me to figure out what to do with them.