As a BGK owner I think it's quite sad that you don't have the opportunity to see the fella in a tank setting - I was watching mine for ages yesterday flitting back and forth attacking the tubifex I'd put in.
I agree with pica, BGK aren't easy to pin down on growth rates, I've had my current one for 3 months and he's probably grown the best part of an inch, but then it was small when I bought it.
Agree with betta pond too, if you've got 1 male and several females, the law of nature will take over, they'll spawn, then you could potentially have 10's per spawn, and you'll probably find 75% are going to be males - then you'll be running into serious problems!!!!!