I have a 15 g tank, 38x38x 40 cm in height, with one male Betta, 10 otocinclus catfish and 4 nerites. Since I'd like to add a bottom dwelling species, i was focusing on Panda cories, which don't grow to large sizes. But I fear i might ruin everything. And if I can add something more, would it be something else? What do you advise me?