okay we talked it over at work... use your 90 as a show tank, and use a small 29ish tank for breeding... One male 3-4 females... oh to tell on fisk flip over and look near anal fin. push it aside... If small you may not see anything on a male, but should be two small holes in a line down the body. A female will have one big and one small noticable difference in size. or if small only one hole... again show tank 90 and breed in smaller... thats what I do... and it works pretty good.
again you keep the change...