If its from a batch of babies there will usually be a larger one that rules the tank ( alpha male) the males tend to grow faster than females is the only way I can tell as of now.
yeah basically. if it grows hella hella slow. it could be female. and colors usually show even when smaller, but some tend to color up at a later age, 2 years and my fh colors are still changing.
Psst! Newsflash! They never stopped growing since being laid as eggs, and it is highly unlikely that they ever will
With that being said, with fish in question a 30 gallon tank will work but for a very limited period of time. If your filtration is good, I'd say 6 months tops, maybe 7
I Have 2 that are 1/2" and than the big alpha male who is 4-5" I'm going to keep about 10 of the ones I actully have now and the rest I'm going to sell. So The smaller ( the better chance its a female)