How fast do they breed? Given the right conditions, prolific may be an understatement. I am not sure how many per brood. I started with 10 last October in a planted 15 gallon tank. I now have over 400! I sold 100 last week and it did not even make a dent in the population.
When I could accurately count them, I had at least 15-20 gravid females at any given time.
I also have tiger shrimp breeding in the same tank.
Full disclosure: I was feeding a bit of NLS pellets along with veggie disks and pellets for the last few months. ( I had corys and otos with the shrimp). It did not seem to affect the shrimp population.
I just noticed two weeks ago the copper content in NLS. That is when I stopped feeding it to the shrimp.