do you have a 20g to put them in first? that would work better i think, then once they grow out pop em in the 75 or 125. .5in is big enough to eat adult brine shrimp, shouldnt need baby brine shrimp (harder to find). they should be on blood worms in a matter of weeks though.
i swear i caught them as a kid out of a pond across the street from Northwoods Country club (off club drive), that retirement home. they dont like you fishing there, and the other side entrance is gated and they used to not mind, but i think they do now.
