Welcome to the forum Marshy.
A lot depends on which fish you have. If you are keeping cichlids, they exercise parental care and you may not need to separate them. If you have livebearers, the adults may well be cannibalistic toward their fry. Unless you are prepared to expand to more tanks, I would suggest that you put some cover into the tank and let whatever fish survive stay on while the rest become supper. I use java moss for livebearers but am now branching out to try najas grass. Many livebearers will have a few survivors from each drop if the fry can find some cover.
