Turquoise Rainbow Question

If you've had these fish for 10 months and they are only 1½-2 inches, then either they are severely stunted or they are not "Turquoise" rainbowfish.

This is the fish that is commonly sold as a "Turquoise":
http://members.optushome.com.au/chelmon/Lacust.htm

However, it is a Lake Kutubu Rainbowfish. Turquoise is a made-up marketing name and not the real name of the fish.

Is that what you have in your tank? Or do you have these:
http://members.optushome.com.au/chelmon/Praecox.htm

The Neon Rainbowfish? Sometimes these are sold as Turquoise rainbows.

Can you post a picture of the fish? I really hope you don't have the Lake Kutubu in your tank, because if you do they are severely stunted. A 50 gallon tank is too small for fish that grow 5+ inches, especially 12 of them.

As for color, most rainbows color up at 6 months, fully color by 10 at least. They are very slow growing fish for the most part.

Hard to say until we confirm exactly what kind of rainbowfish you have.

Roan