I believe u will find it difficult to keep tigers together. I've tried many combos and there is always one that is the aggressor. Ur better off concentrating one one specific fish. I presently have a gatf around 16" by himself with limited stock with him/her. Plenty of swimming space min decor. Along with good water current. High o2 too. My opinion is u stick with one or the other. Swapping out for a different atf will eventually lead down the same rd. Schools of 5 or more are best if that is ur choice. 2 of 1 and 1 of another is futile.