I had 10 CRS in a 1.5 gallon tank sitting on my desk at work and they bred. Got as many as 30 juvies before I sold them to Ocean Aquarium in SF.
The key was keeping the water clean by using fast growing stem plants like hornwort with medium/high lighting. That kept the nitrates at near undetectable levels.
So my guess is in a 2.5 gal, you could keep like 40 adults, but you'd have to make sure that you either do water changes often, or keep fast growing stem plants.
Last edited by genetao; 01-31-2013 at 08:13 AM.
Reason: More info