I had one that looked just like yours and didn't harm a thing until it got around 6-7 inches, then it quickly had to get traded to the LFS for credit. Seriously, I have never seen a rd like your not turn out to be aggressive. I thought the same thing about mine and thought I had gotten lucky, then she went balistic.
Here is what she looked like when young, and then when she got bigger.
Here is what she looked like when young, and then when she got bigger.
In six months there will be a whole load of ass kicking in that tank and the Rd will be the one doing it