I've had these two male fancy guppies for a little over a month, where they've lived peacefully with two zebra danios. This weekend I added two glass catfish and a velvet swordtail. The guppies (one more than the other) is constantly harassing the swordtail (who is bigger) by kind of picking at him and swimming extremely close to him. What should I do? It doesn't really seem to be hurting the swordtail, but I don't want him to get too stressed.