I once had about 16 harlequin that had to share a tank with 3 pictus for a few days, by the time the pictus tank was ready for them to go into, I was down to about 5 harlequin. When the pictus are full grown be cautious, I've read stories of pictus eating smaller corys. I just have my pictus in a tank by themselves besides for the oscar thats now in it