Humm until you can post some pictures of fish, numbers, dimensions of tank, ph, temp ext, it would be hard to tell. sounds like it will take on dramatic change specially if you have mixed mbuna or having SA or NA together, once cichlids start to mature, some spawn as little as 1.5 inches.
The yellow you mention could be yellow lab or aka electric yellow. here is a picture of a tank I had a year ago, the yellow lab in middle is a hybrid, with pale on underside, purchased at LFS, so I know its not pure. Tthe other ones are breeder order more pure. If you have blue with yellow fin (its a p.acei) these cichlids are semi aggressive and u need a ratio of 1m 4/5females. if you do have these the only positive is you have a 75 gal. If I read right you have a goldfish in there?? if you do wow that needs to be rehomed different care requirements, plus massive bioload.